Your question functions on several levels. On the plane of halachah (Jewish law), the first concern that arises is that the Torah explicitly forbids a person that is not Jewish from partaking in the Pesach sacrifice that is eaten at the seder meal (Shemot/Exodus 12:43.) However, we no longer have this sacrifice today since the Temple in Jerusalem was destroyed and so many do not consider this meal restriction to be in effect today. However, the Shulchan Aruch (Orach Chaim 512:1 and the commentary of the Mishnah Berurah there) limits cooking that may be done on a Yom Tov holiday to cooking that is done in order to feed Jewish people. This would seem to impinge on one’s ability to invite over someone who is not Jewish and have cooked food for them to eat. There are several ways to deal with this concern, including the suggestion that if all the food was already cooked before the Yom Tov and now is only be reheated then it is fine (Teshuvot B’Mareh HaBazak 3:56.) Alternately, one could cook a large quantity of food for all the guests and have plenty to go around for all that arrive (as opposed to specifying a portion that is cooked for the Gentile.) Another concern that is raised centers around the prohibition of teaching Torah to someone that is not Jewish (Talmud Chagigah 13A), and there is a great deal of Torah study involved in a seder meal. This too need not necessarily be a concern, as Rabbi Moshe Feinstein ruled that it is permitted to teach Torah to Jews while a non-Jew is sitting there and listening (see responsa Igros Moshe, Yoreh Deah 2:132). As such, the fact that your friend is present need not be of concern since there are other Jews there already to learn and share at the seder. A separate concern raised in that same responsum by Rabbi Feinstein would involve the wine that is served for the four cups that we drink at the seder. Wine is a sacred food that was used in the service in the Temple and is subject to special restrictions. As a result, wine that is not “mevushal” (flash pasteurized) and thus could have been appropriate for Temple usage may not be poured by someone who is not Jewish. But there are many kosher wines available on the market that are indeed mevushal and would not pose any problem. On a philosophical level, the seder is an awkward place to host someone who is not Jewish. There are those Jewish holidays that have a universalistic orientation, such as Rosh Hashanah when we pray on behalf of the entire world. Similarly, Sukkot involves our hopes and requests of Hashem that the entire world be blessed with rain and abundance. However other holidays, such as Pesach, are especially particularistic and focus on us as a special and separate people. Inviting someone who is not Jewish to a meal that celebrates our being saved from the hands of oppressive Gentiles could have sensitive moments, especially as the focus shifts to the oppressions that we have endured through many generations up until the present and our hopes for future redemption. This is very much a meal of celebration that focuses on our being in many ways apart from the rest of the world. Of course, all of the above assumes that your son is comfortable with your inviting others to his seder. Otherwise there is a family and interpersonal issue that should be considered as well.

You ask a painful and delicate question, one that is almost certainly best posed with all of its accompanying circumstances to a knowledgeable and sensitive rabbinic authority. That said, and in the absence of the details of the particular case, two operative principles may be noted as relevant here. At face value, the answer to the question is “no”. The Talmud (Tractate Sotah, also Ketubot) presents as a matter of legal principle and tradition that a woman who commits adultery may not remain married to her husband nor may she marry the man with whom she has committed the affair. She is forbidden to both of them, even after a proper divorce has been completed with a gett. This is codified as law in the Shulchan Aruch, in section Even HaEzer 12:1. However, there is a complicating factor that comes into play as far as applying the abovementioned principle in practice: verifying to the satisfaction of Jewish law that the affair has indeed taken place. While in monetary matters a simple admission of guilt can create a legal obligation to pay, this is a result of a person’s ability to bind himself into most any financial commitment of his or her choosing. However, in non-monetary matters such as ritual or sexual commandments, a person’s own admission of guilt is not accepted as legally compelling. This principle of “A person cannot [via admission of guilt] cause himself to be considered wicked” is found in the Talmud in Tractate Sanhedrin 9B and is codified as law in the Shulchan Aruch in section Choshen Mishpat 34:25. It effectively means that in areas of Biblical prohibition (some say that this applies to Rabbinic prohibitions as well) one cannot legally incriminate oneself through confession of guilt. In order to be sure that an affair has taken place, Jewish law requires either the testimony about the affair of two kosher witnesses that are related to none of the parties involved, or alternately the testimony of two witnesses that the husband warned his wife not to go into a secluded place with this man and then testimony that she indeed did so. These circumstances are far less common, and as a result it is very difficult to establish with legal certainty that adultery has taken place (and that the subsequent marriage is forbidden) even if it is excruciatingly clear on a personal level.

While you are correct to surmise that Jewish tradition tends to focus on the here-and-now and making ourselves the best that we can be in this life, there is quite a bit in traditional Jewish sources about the nature of the afterlife. Primary initial references and descriptions may be found in the Mishnah in Pirkei Avot, numerous passages in the Talmud (particularly Tractates Shabbat, Rosh Hashanah and Sanhedrin), and the works of classical commentators such as Maimonides (see laws of repentance chapter 8). For an excellent brief essay and overview of the topic, you may want to look at the essay entitled “Immortality and the Soul” in Rabbi Aryeh Kaplan’s book If You Were God. While there are variations offered on the primary themes, the core concepts of the afterlife stem from the notion that a human being is an amalgam of two very different aspects: a body and a soul. For the course of a person’s lifetime, the two work together in marvelous coordination. The body functions as the vehicle or tool that allows the soul (which holds the thoughts and persona and higher levels of existence of this human being) to interact with and impact the world around us. At the time of death, the body and soul separate. The body, beloved and respected for having been the shell that held a holy soul, is laid to rest in the earth like any other precious and holy item in Jewish tradition. The soul is non-physical, and as a result lives on. The cessation of respiration and bodily function do not affect it at all. The soul continues in a non-physical existence with no physical needs or sensations. No hunger, no cold, no pain, and no exhaustion. Perhaps the best way to describe the nature of that existence is one of exquisite awareness. First and foremost is awareness of one’s deeds during life and the totality of their impact on the world (Sefer HaIkkarim of Rav Yosef Albo). This is a sublime and wonderful experience, as one is aware in a way as never before of exactly how each little positive action helped others and changed their lives. Through good deeds we contribute physically and metaphysically to a better universe, but only after the soul is freed from the confines of a physical body is it truly cognizant of this. However, this can also be a very difficult experience to the extent that a person’s actions were negative and destructive. (It is comforting that the Mishnah in Eduyot 2:10 states that this difficult period of recognizing and reconciling one’s mistakes lasts up to a maximum of twelve months for all but the worst human beings.) Thus it would be fair to say that what others call “heaven” and “hell” are to Jews the same existence; it is knowing very well what our lives amounted to, and that can be a very good or very bad thing and likely some of both. There are sources that suggest that one may well have a sense of connection and awareness of deceased loved ones, as well as some degree of awareness of events happening in this world for those close to us. Reincarnation is debated in classical Jewish sources, with Maimonides clearly of the position that we live only once in this material world, while Nachmanides and the Kabbalists indicate that many people come back to live here again in order to finish up their lives’ missions. Every one of us began this life in the womb, in an existence that is so startlingly different from our own as to be unrecognizable (living curled up in liquid, not seeing very much, eating through our umbilical cord, etc.). After nine months we emerged into a radically different experience that is now so familiar to us. After our time here, our tradition teaches that we move on to a next and even greater stage of life.

In Jewish law one is not permitted to visit a place of idolatrous worship, let alone show any deference to it (Rambam/Maimonides in his commentary on the Mishnah tractate Avodah Zarah chapter 1, also quoted by the Shach in Shulchan Aruch Y”D 149). As a result, the answer actually depends on the status of the faith or belief system in question. Religions that worship multiple deities generally fall neatly into the Jewish definition of idolatry. According to many commentators (including Maimonides) the same applies to Christianity. The concept of the trinity, along with the worship of a human being as god, is understood as qualifying the Church as a place of idol worship. However there are those such as the Meiri, that disagree. He maintains that while Christianity is not a correct belief and completely forbidden for a Jew, it is not considered idol worship. Similarly, later commentators offer further consideration of the different denominations of Christianity such as those that do not believe in the trinity. Islam is universally recognized as monotheistic and non-idolatrous, and so entry into a mosque is permitted (though a Jew may not pray the prayers of another religion). It is worth noting that entry into a forbidden house of worship through a side door for purposes that have nothing to do with religious ceremony, such as when a Church is using as a polling station for voting and elections, is permitted. Also, if the faith is no longer in existence, such as the ruins of a religion that is no longer practiced, many permit entry. In terms of the theory behind the restriction, most point to distancing ourselves from beliefs and practices so antithetical to the fundamental tenets of our religion. The issue of temptation to worship is raised as well. Human beings seem to have a tendency to associate beauty with truth; when we enter into a beautiful cathedral, it is natural to begin connecting with it as a correct idea even if we know on an intellectual plane that we disagree.

Your question raises many sensitive concerns, including the tension that can arise between following the laws of one’s locale as well as Torah law, not to mention potential tensions with neighbors and community associations and the possibility of making Jews look like we somehow feel “above the law”. The principle of “dina d’malchuta dina”, that “the law of the land is the law”, does indeed mean that Jewish People have a halachik/Jewish-legal obligation to abide by the laws of the country in which we live. To directly address the concern raised, the Shach (in Shulchan Aruch Chosehn Mishpat 73:39) states clearly that the rule of dina d’malchuta dina does not apply if it directly contravenes Torah law. That is to say, one has a mitzvah to place a mezuzah on their doorpost, and (short of a threat to one’s life) that mitzvah overrides a local law. However, this case does not appear to be one of dina d’malchuta dina in any case, as it isn’t a law of the government but rather that of the condo association. The Ramban (Bava Batra 55A), Ritva, Tur (Choshen Mishpat 369) and others all note that in order for a rule to be considered dina d’malchuta dina, it must be an established law of the land that is well known to the people of the kingdom, found in the statute books of the kingdom and equally applied in a non-discriminatory way to all the citizens. It seems unlikely that the association of a condominium group qualifies as a government, nor that the other conditions are fulfilled in the case. Thus, this may indeed be less of a dina d’malchuta dina case within Jewish law than a first amendment case within US law about the ability of those who regulate properties to restrict religious expression.

While the approach is somewhat nuanced, on the whole Jewish tradition is quite supportive of environmental protection and friendliness. It begins with recognizing an inherent tension between human societal development and responsible stewardship of the earth. The verse in Genesis/Bereishit 1:28 directs humanity to “conquer” the land. Ramban explains this as a mandate to use the world to our benefit, and the example he offers is mining copper out of the ground. Yet at the same time, Genesis/Bereishit 2:15 charges Adam with protecting the Garden in which he lives. Humanity is from the beginning of time placed in the role of guardian that cares for the earth, for it does not belong to us. "The earth and all that is in it belong to G-d” (Tehillim/Psalms 24:1). Additional verses found in Deuteronomy/Devarim 20:19-20 offer further clarification. In the context of war and laying siege to an enemy city, the Torah prohibits the cutting down of fruit trees to make battering rams or to cause the enemy dismay. Rather, we are instructed to use non-fruit bearing trees. The Sefer Hachinuch (mitzvah #529) explains that this prohibition against needless destructive impact is not just for trees, but rather for the needless destruction or waste of any item. Human beings are allowed to make use of the environment, but only with legitimate cause and with care not to cause undue damage. For example, while as a rule the saving a human life trumps concerns of ecological impact, the Shulchan Aruch (Choshen Mishpat 155) places limits on industry that causes pollution to a city. This delicate balance is well put by the Midrash Kohelet/Ecclesiastes Rabbah 7: “When Hashem created Adam, He took him and showed him all the trees of the Garden of Eden and said to him, ‘See my works, how beautiful and praiseworthy they are. Everything that I created, I created for you. Be careful not to spoil or destroy my world, for if you do - there will be nobody after you to repair it.’”

It is worth noting that the nature of the protection that we received during those years in the desert is debated in the Talmud (Tractate Sukkah 11B). In that source, Rabbi Eliezer is of the opinion that sukkot recall the protection offered by the clouds of glory (ananim) that you mention. However, Rabbi Akiva disagrees and suggests that during those years we sat in man-made desert huts and that our sukkot are built to remember those shelters. It is within this approach of Rabbi Akiva that your question resides. There is another unusual dimension of this holiday that may shed some light here. Other Jewish holidays take place on a specific date, the date on which the event that they commemorate took place. Sukkot, however, is not about a particular day of the year. It commemorates a life that was led in the desert with Hashem’s protection over a span of forty years. In essence, the events that it recalls took place every day of the year for four decades. The Talmud offers reasoning for celebrating it in the fall, but the miracle it represents was indeed daily. In that sense, Sukkot can be seen as celebrating the constant protection of Hashem, a daily protection from the elements and from the dangers of desert wildlife. It thus makes sense that the holiday might celebrate God’s protection through a man-made structure, because the focus is not on miracles of noticeably large and impressive nature as much as on the moment to moment protections that Hashem offers us every moment of each day that we live. It is a holiday of small constant miracles that mix their way into our lives and often go almost unnoticed.

The fact that the topic in question is tznius (modesty) makes things even a bit more complicated, as there are multiple aspects to this mitzvah.  First, the mitzvah has both an objective as well as a subjective element to it.  As an example of objective immodesty, the Gemara states (Berachos 24A) that a woman’s thigh is considered to be an area that must be covered.  There is some debate as to whether this applies below the knee, and the Mishneh Berurah rules (Orach Chaim 75, note 2) that it is not necessary to cover below the knee.  However, the Mishneh Berurah notes subjective tznius factors as well, including local custom.  Thus there are parts of the body such as the upper thigh and chest that must be covered in public no matter where one lives and what the circumstances are, while others such as below the knee and sleeve length often depend on circumstance.

 

It is critical to note as well that modesty refers to a great deal more than length of fabric, as its fundamental focus is upon not making oneself an unnecessary center of attention.  One should look at the style of the clothing - is it tight and flashy or more quiet and unassuming?  Dress is only one dimension of modesty: tznius also very much applies to behavior and speech.  Does one act and speak in a way that draws attention without cause?

 

One of the first steps that the great Poskim (halachik deciders) utilize in such conflicts of values is to consider whether there is a way to frame the situation that the values need not be in conflict in the first place.  To wit, are you actually being asked by your mother to violate the mitzvah of tznius?  Is she requiring you to wear shorts or tank tops during the summer?  Many women who are meticulous about the mitzvah of modesty and live in warm climates wear lightweight fabrics that cover their bodies without being overly uncomfortable in hot weather and find that one or two layers is quite sufficient. Might there be solutions that would allow you to adhere to your values of dressing modestly while allaying your mother's apparent concern about your well-being?  If you are able to have a conversation with her in which you let her know that you care about her concerns and would like to try and find a way to respect them, she may have ideas that are acceptable to you. By asking the question in a respectful way, you will also be demonstrating the idea that "the ways of [the Torah] are pleasant" and will be fulfilling the mitzvah of Kiddush Hashem (sanctifying Hashem’s name) at the same time that you fulfill the mitzvah of honoring your parent.