1)
Why does it say "Min Bnei Chayil"?
1.
'Rashi': At this time they gathered for war with the Hagri'im. Malbim - this is like in the Midbar, they were counted according to their fathers' house "Kol Yotzei Tzava b'Yisrael."
2)
What is the grammatical form of "Lemudei [Milchamah]"?
1.
Radak: It is an adjective. Lamad is Po'el Omed (the subject himself acts). It does not have a Pa'ul conjugation (one who was taught).
