Ta’anit Esther this year will be Thursday, March 9th. What time does the fast begin and when does it end?
The fast begins when one goes to sleep at night, unless one plans to wake up early to eat before the fast begins. If one planned to wake up early, he can eat until alot ha’shachar (dawn)  which is 72 minutes before sunrise. The fast ends at tzeit ha’kochavim, nightfall. (There are different opinions regarding when tzeit ha’kochavim occurs. Rav Moshe Feinstein evaluated that it is 50 minutes after sunset, but if one is having difficulty fasting, he may break the fast 40 minutes following sunset.)
Most years, Megillah reading follows maariv at the end of the fast. It is then preferable to refrain from eating until after hearing the Megillah. If one is having a difficult time fasting, especially if he/she is waiting to hear a later reading of the Megillah, one may eat a snack after tzeit ha’kochavim. If one is very weak and needs to eat a meal, they may do so, but they should assign someone to remind them to hear the Megillah .
This doesn’t apply this year. As Purim is on Sunday, and fasting is prohibited on Shabbos, the fast is moved from Shabbos to the preceding Thursday. The fast won’t be followed by Megillah reading, and eating will be permitted immediately after nightfall. Shulchan Aruch O.C. 564:1
 Mishnah Berurah O.C. 692:16
Who is obligated to give a Machtzit Hashekel and when should it be given?
When the Temple stood in Jerusalem, there was an obligation in the month of Adar for every adult male to contribute a half-shekel coin toward the purchase of the upcoming yearly communal offerings. Today, as a remembrance of those coins, a machtzit hashekel (half dollar coin) is given to charity. Since the word “shekel” is repeated in the Torah three times, the common custom is to donate three half-dollar coins to charity.
There is a difference of opinion as to whether all men from age thirteen are obligated, or only from the age of twenty. However, many have the custom that young men beginning at age thirteen give the machtzit hashekel, and fathers give the machtzit hashekel on behalf of their young sons before the bar mitzvah age . The coins are contributed on Ta’anit Esther before Mincha, but if they were not given then, they may be donated anytime afterwards as well . Mishnah Berurah O.C. 694:5
 See Teshuvas Avnei Yashfeh O.C. I:133
Can one fulfill their obligation of Purim seudah (festive meal) on the first night of Purim?
The mitzvah to eat a seudah on Purim is specifically in the day. However, it is proper to eat a partial seudah at night as well , and it is customary to eat seeds or grains on Purim night to remember the difficulty that Esther had in eating kosher when she was in the palace . Shulchan Aruch O.C. 695:1
 See Yalkut Yosef KS”A O.C. 695:18
Earliest/latest time to read the Megillah on the day of Purim?
The Megillah can be read anytime during the day of Purim, from sunrise until sunset ; however, to show our enthusiasm for the mitzvah it is proper to read the Megillah as early as possible. In cases of pressing need, one can read the Megillah from alot hashachar (dawn, 72 minutes before sunrise), but it may not be read any earlier. If one still had not read the Megillah by sunset, they should read the Megillah without reciting the beracha. 
 Shulchan Aruch O.C. 687:1
 Mishnah Berurah O.C. 687:5
What are the guidelines for mishloach manot?
Both men and women are required to fulfill the mitzvah of mishloach manot. One must send two different portions of food or drink to at least one other Jew. The foods should be ready to eat items (e.g. not raw chicken, meat or fish) that one would typically serve at the Purim seudah. The items need not be foods with different berachot.
For example, one may send as mishloach manot an apple and an orange. While there is no specific size or value for what constitutes a portion, some authorities maintain that the portions must be considered important by the receiver . Therefore, one should not send a wealthy person a portion that he would consider inferior. It is proper to send “shalach” manot (a common slang usage), as the name implies via a messenger . Beiur Halachah 695 s.v. Chayiv
 Mishnah Berurah O.C. 695:18
What are the restrictions for an aveil (one who is in their year of mourning the loss of a parent or thirty days of mourning the loss of other close relatives) regarding sending and receiving mishloach manot?
Everyone is obligated to fulfill the mitzvah of mishloach manot, including one who is in mourning. However, because these gift baskets are associated with extra happiness, which is an unfitting display for one who is in mourning, the mishloach manot should be scaled back to the minimum. The mourner should send only one package of mishloach manot, and it should contain simple foods that do not give the appearance of a celebration . Additional mishloach manot can be sent by the family without designating the aveil specifically.
Likewise, it is considered improper to send mishloach manot to a mourner. Instead, one should address the mishloach manot to the family. However, some permit sending mishloach manot to a rebbi or teacher who is in mourning, since in this case the gift is viewed more like a payment or a tip . If mourners did receive mishloach manot, they may accept the gift . Mishnah Berurah O.C. 696:18
 Teshuvas Divrei Malkiel V:237
 Teshuvas Shevet HaLevi X:107
What are the guidelines for matanot l’evyonim?
Every Jew is obligated to give gifts to two needy individuals. All men, women and children over the age of bar or bat mitzvah are obligated in this mitzvah, even if they do not have their own income, and even if they themselves would qualify to receive these gifts . It has become customary for rabbis and other community leaders to collect funds on behalf of needy individuals. Monies can be given to these collections before Purim, provided the funds are distributed on Purim.
While there is a difference of opinion as to the exact minimum amount one can give to satisfy their obligation, (a few pennies or a few dollars), it is well known that the Rambam (Megillah 2:17) writes that it is better to increase the amount one gives to matanot l’evyonim even more so than for the Purim seudah or mishloach manot. Additionally, there is a custom that on Purim anyone who puts out their hand for assistance should not be turned away empty handed. Mishnah Berurah 694:1
How should one conduct himself with respect to drinking on Purim?
While there are different halachic opinions regarding drinking on Purim, clearly, the safety of you and those around you takes precedence. One should exercise proper discretion. The OU does not condone underage drinking. Furthermore, excessive drinking is inappropriate. One must be vigilant in preventing any trace of chilul Hashem from inappropriate behavior on Purim.
If I began my Purim seudah during the day, but it did not finish until after tzeit ha’kochavim, do I still recite Al Hanisim in bentching?
Yes. However, there is an opinion that if one already davened Ma’ariv, then they should no longer recite Al Hanisim in bentching. Therefore, to avoid this question, it is proper to bentch before davening Ma’ariv. (Mishnah Berurah O.C. 695:16)