1)
Who are "Kol ha'Nosar"?
1.
Radak: Those who put to their hearts in the war, and will return to Hashem with all their hearts.
2)
What do we learn from "l'Melech Hashem Tzevakos"?
1.
Radak: They recognize that He is king over the entire land.
3)
Why does it specify Sukos?
1.
Rashi citing Avodah Zarah 3a: At the end of days, Nochrim will request Torah, to observe it. Hashem will answer, I will give to you an easy Mitzvah, i.e. Sukah.
2.
Radak, Malbim: The war will be during Sukos. They will see the Creator's miracles, and come each year at that time to commemorate them.