1. RAMA: It is a mitzvah to many feasts during Purim (Tur), but one fulfills his obligation with only one feast (Mordechai) One who does the Purim meal at night does not fulfill his obligation. RAMA: Nevertheless, one should be happy and add more during his meal even at night (Teshuvat Mahariv).
2. One is obligated to be intoxicated on Purim to the point where he does not know [the difference] between "accursed is Haman" and "blessed is Mordechai". RAMA: Some say it is not necessary to become drunk so much, but rather to drink more than he is used to (Kol Bo), and to fall asleep, and while he sleeps he does not know [the difference] between "accursed is Haman" and "blessed is Mordechai" (Maharil). [There is no difference on Purim] between one who has more and one who has less, as long as his heart is directed to heaven. One should not fast on Purim, except for a fast for a [bad] dream, and see earlier Siman 568 and Siman 570. There are those who have the custom to dress in Shabbat/Yom Tov clothes on Purim, and that is correct (Maharil). We have the custom to make the Purim meal after the afternoon prayer, and pray the evening prayer at night. We pray the afternoon prayer while most of the day remains, and most of the meal needs to be during the day (Minhagim). And it should not be like those who have the custom to start close to evening, and most of the meal happens during the night of the 15th. When Purim falls out on Friday, they should have the meal in the morning because of honor for the Sabbath (Minhagim). And one who wants to [have his meal] every [Purim] in the morning is allowed to (T"H). Some say that there is [significance] to eating seeds on Purim as a remembrance for the seeds that Daniel and his friends ate in Babylonia (Kol Bo). It is good to delve a bit in Torah before one begins the meal, and a support for that is (Esther 8:16) "The Jews had light and happiness...", which we learn out "radiance" - that's Torah (Mahariv). One is obligated to drink a little and be a little happy on two days, the 14th and the 15th (Minhagim), and so is the custom. And some say that if one causes damage to his fellow through his happiness on Purim, he is exempt from restitution (Terumat HaDeshen, Part I 110). And see Terumat HaDeshen Laws of Damages.
One says "Al hanisim" in the Grace After Meals during the blessing of the land ["Nodeh"]. And if one started his meal during the day, and extended it into the night, he [still] says "al hanisim", for we follow the [status of] the beginning of the meal. And some say one should not say it. (And we have the custom like the first opinion).
One must send to his fellow two portions of meat, or foodstuffs, as it says (Esther 9:19) "And send portions, man to his fellow." Two portions to one man [is the obligation]. And anyone who send more to his fellows is praiseworthy. If he has none, he can trade with his fellow, this one sending to that one his meal, and this one sending to that one his meal, so that they can fulfill "And send portions, man to his fellow." RAMA: And some send the portions during the day and not at night (from the Rosh, first chapter of [Bavli] Megilla). And if one sends portions to his fellow, but he doesn't want to accept them, or he forgives him [his obligation], he fulfills [his obligation nonetheless]. And a woman is obligated in [sending] portions to the destitute and sending portions [to one's fellows] like a man is. A woman sends to a woman, a man to a man. But not the other way, so that a man does not come to send it to a widow, and it will come to a possibility of kiddushin [having been enacted]. But portions to the destitute one should not worry [about this possibility].