Clarifications about the rules

[Ugin87]

Hello everyone, I am a new player of AotP and I have some questions about rules:

1- every battlefield tells you how much armies can you bring on it at the beginning of the game. Can I choose anyone of the armies I have? for example can I choose a planeswalker and 2 or more squad creatures? Oblviously mantaining their total value above the limit

2- how does "action 2" work? I have to choose only ONE army cards, so I can use (in that turn) only my planeswalker OR a squad OR a hero? And so, can I move and attack only with the one I choose?

3- if my planeswalker is destroyed, how can I bring it back into the game?

I m waiting to play the first game with this boardgame, so I hope there will be no other doubts; but in that case I'll write again. Thank you very much, bye