Why did the northern wind blow exactly at midnight?

Aruch: The Gemara in Bava Basra 25a states that there are four winds that blow every day, each at a specific time. The eastern wind blows from the morning until midday. The southern wind then blows until the night. The western wind then blows until midnight. And the northern wind then blows from midnight until the morning.

Yaaros Dvash (1:15): It was miraculously done by Hash-m to show His favor towards David.

Why did David not offer to sustain the people at that time himself?

Yaaros Dvash, Imrei Emes (Likutim Brachos 3b): When David defeated Golias, all of the Jewish girls threw silver and gold to him. He took all that wealth and set it aside to use for constructing the Beis haMikdash. When the people needed money, David refused to use that wealth to support them and instead chose to wage optional battles against the enemies. Hash-m criticized David for this, saying (Divrei haYamim I 22:8), " דם לרב שפכת ומלחמות גדלות עשית לא תבנה בית לשמי" - "You have shed much blood, and you have waged great wars; you shall not build a House in My Name". (And in fact, in Melachim I 7:51, Rashi writes that for that very reason, Shlomo did not want to use that money, since it should have been used to support the people during the time of famine.)

Did this conversation between David and the Chachamim take place every day?

Ritva: No; only when the people were very poor and there was a great need.

Tapuchei Zahav: It was every day. Even though they had already had the same conversation the previous day that eventually resulted in the permission to wage war, they would check it again each day. This concept is discussed in Mesilas Yesharim (end of Perek 6). When a person finds a leniency, he should carefully check its validity and only then act.

Imrei Emes: It was every day. Since David had studied Torah all night, he had become detached from his physical side and forgotten the physical needs of Klal Yisrael. The Chachmei Yisrael therefore needed to remind him each day of the needs of the people, so that he could bring them blessing from above. (The Sfas Emes earlier wrote (Parshas Va'eira 5638) that this is not so hard to understand. If we see that the evildoers can forget in this world that their Neshama comes from above, all the more so can a Tzadik forget that he has a physical side!)

Why did this conversation take place 'as the light of dawn rose'? Was there not an obligation for David to recite Kriyas Shema and Shemoneh Esreh before accepting visitors?

Tzitz Eliezer (22:76) citing 'a Kadmon': One can assume that the Chachamim entered before the king in a way of subjugation and humility and with bowing. David actually used their visit at this time as preparation for his morning prayers. He would see their reverence before him and use it to properly present himself before Hash-m, just as one would before a king.

What is the meaning of 'a Kometz does not satisfy a lion'?

Rashi (Berachos 3b with the text of the Bach): A handful of grass does not satisfy a lion.

Rashi (2nd Peirush there): (Eating) a grasshopper (Kumtza in Aramaic) does not satisfy a lion.

Rav Hai Gaon (cited in Tosfos haRosh): Kometz means a pit in Aramaic (as in Targum on Shmuel II 18:17) - a lion in his pit does not get satisfied (from the pit itself).

Tosfos haRosh, Ritva: When a lion is hungry, it sucks its fist. Doing so does not satisfy it.

What is the meaning of 'a pit cannot be filled with its Chulya'?

Rashi: If one uproots the dirt of a pit and attempts to return it, it cannot fill it.

Tosfos (Yesh Meforshim): 'Chulya' is the dirt that is put around the edge of a pit as a lip. If one would push that into the pit, it would not fill it.

Tosfos (R' Tam): A Chulya is a source of water of a pit. The source cannot fill up the entire pit. Another water source must also be used. (The Margalios haYam points out that this explanation can be seen explicitly in the Midrash of Sefer Shmuel 27:3, where it states, "R. Yochanan said - HaKadosh Baruch Hu said to David, 'David, a pit is not filled from its 'Chulya' unless a stream of water is drawn from nearby'".)

Tosfos (Ri in Tosfos Berachos 3b): If one takes dirt from one side of a pit and places it on the other side, the pit will not be filled as it is now lacking on the first side.

Why did they first ask Achitofel and only then consult with the Sanhedrin?

Malbim (Eretz Chemdah, Likutim end of Vayikra): One should first devise a practical plan (as a way of making natural effort - Hishtadlus) and then ask of the Torah if it is permitted.

Why did the Chachamim consult the Sanhedrin first? Why not go straight to the Urim ve"Tumim?

Nofes Tzufim (Brachos 3b): Rashi explains that they would ask permission of the Sanhedrin so that they would pray for them to be successful in the war. These prayers could potentially change for the better the answer that the Urim ve'Tumim would give. Without the prayers of the Sanhedrin for the success of the war, perhaps the Urim ve'Tumim would answer that they should not go out to war.

Nofes Tzufim (2nd answer): Tosafos in Gitin (68a, dh Zil) state that the Urim ve'Tumim should only be consulted when absolutely necessary, to avoid relying on miracles. In the case of war, the Sanhedrin's approval was required first. If the Sanhedrin disagreed, then they would turn to the Urim ve'Tumim. So, it was better to first ask the Sanhedrin before resorting to the Urim ve'Tumim.

The Pasuk from Divrei haYamim I 27:34 seems to be quoted wrong, as the Pasuk actually refers to "Yehoyada ben Benayahu" not "Benayahu ben Yehoyada"?

Rashi: The Gemara's text is correct.

Binyan Shlomo: Rashi could be explained as follows. Although the Pasuk seems to state that Yehoyada was Benayahu's son, it is actually the opposite. There is a Pasuk in Divrei haYamim I 2:50 that states, " אלה היו בני כלב בן חור". It appears to mean, 'These were the sons of Kalev, the son of Chur". But Rashi there comments, " היו בני כלב בן חור כמו בנו חור" - "'son of Chur' is like 'his son was Chur'. So too here, 'ben Benayahu' means that 'his son was Benayahu', meaning that it was Benayahu son of Yehoyada.

Tosfos: The correct text is 'Yehoyada ben Benayahu'. If so, how does the Gemara prove that Yehoyada was the Sanhedrin from his father, Benayahu's, position? It is logical to say that Yehoyada ben Benayahu filled the role of his father, Benayahu ben Yehoyada.

According to the Gemara's understanding that David would sleep until midnight and then be woken by the harp, why does the Pasuk about the harp (Tehillim 57:9) use the word 'עורה'- 'Awake' twice?

Maharsha: The Gemara in Berachos (3b) tells us that until midnight, David would study Torah while dosing like a horse. At midnight, he would then stand up like a lion and learn until dawn. There are three types of 'awakening' (and they are discussed in that Pasuk in Tehillim) - a) a person awakens himself; b) a person awakens himself through something external; c) a person awakens something external. The Pasuk's first 'Awake' refers to David awakening himself in the first half of the night (when he learned, albeit while dosing). The second 'Awake' refers to being awoken through the harp at midnight. Then, at the end of the night, David awoke something external, namely 'the morning'.