Why does it say "va'Eshlachem"?
Malbim: In Yeri'as or Hashlachas Goral, he casts it from his hand without perceiving what is written on it, e.g. "Hipil Pur" (Esther 3:7). That is a chance Goral. Here, the lottery was based on Hashgachah; Hashem made it come up the proper way. It says Yipol
What is the meaning of "l'Fi Nachalasam"?
Rashi: The seven portions should be according to the size of the seven Shevatim that still need to receive.
Malbim: Yehoshua knew that via Ru'ach ha'Kodesh, the Sheluchim will choose the portions that are destined for the remaining Shevatim.