What is "Mishteh"?
Rashi: The entire meal is called Mishteh due to the wine, which is primary.
Why did Esther invite him to a Mishteh, and not say her request immediately?
Vilna Gaon: I have a big request. If I saw it immediately, perhaps you will not agree. During the Mishteh, when your heart is merry, I will request.
Refer to 5:4:3:1, 2, 6-8, 10-12.
Why did Esther invite Haman to the Mishteh?
Torah Temimah citing Megilah 15b #1: She set Pachim (traps) for him - "Yehi Shulchanam Lifneihem l'Fach".
Torah Temimah citing Megilah 15b #2: "If your enemy is hungry, feed him bread. (? You scoop coals on his head)."
Torah Temimah citing Megilah 15b #3: This was lest Haman take counsel and rebel.
Torah Temimah citing Megilah 15b #4: It was lest they know that she is a Yisraelis.
Torah Temimah citing Megilah 15b #5: It was lest Yisrael say 'we have a sister in the palace' and slacken from prayer.
Torah Temimah citing Megilah 15b #6: It was so Haman should be always available to her (to make him stumble).
Torah Temimah citing Megilah 15b #7: She thought, perhaps Hashem will feel (my disgrace that I need to flatter a Rasha) and do a miracle for us.
Torah Temimah citing Megilah 15b #8: She planned to get herself and Haman killed. (The custom was to cancel a decree if one of the authors died.)
Torah Temimah citing Megilah 15b #9: Achashverosh is wishy-washy (if he agrees to kill Haman and does not do so immediately, he might change his mind).
Rashi citing Megilah 15b #10: She wanted that the king and ministers will envy Haman. Rashi - she wanted the king to think that Haman loves her, and he will kill Haman.
Torah Temimah citing Megilah 15b #11: "Pride precedes a fall."
Torah Temimah citing Megilah 15b #12 1 : "I will set their feasts with poison" (the wicked are punished through their feasts. (Maharsha - she wanted Haman and Achashverosh to be punished.)
Kol Eliyahu: [According to the opinion that she became Nidah - Megilah 15a], it was in order to be between him and Achashverosh. This causes one of the men to die 2 (if she is beginning Nidah), or [at the end of Nidah] causes them to quarrel (Pesachim 111a). Also this will nullify the decree!
Malbim: (a) She did not want to the king to think that she wants to kill Haman due to personal hatred. Inviting him shows that she seeks only to save her nation. (b) Her claims against him should be sudden, and he will not have time to arrange his claims. At a Mishteh, the king will be [influenced by the wine, and] easy to anger and make a decisive judgment. (c) After Mazal reaches the highest point, it begins to descend. Haman had the ultimate success; he lacked only kingship. She raised him also to this (refer to 5:12:1:1), so he would fall afterwards.
Why did she say "Asher Asisi Lo"?
Refer to 5:8:4:1-6.
Malbim: It is already prepared. She said so to hasten his coming.