...im a casual magic the gathering player for 15 years now and i own WoA i like the mecanics and DM less factor...
That's great! Pick a faction you would like to add to WoA. Each set contains the cards needed to add the creatures to the D&D Adventure system.
One box allow a 2 player game?
Yes. Each box is designed to teach the game to two players.
What is the best to have all of them, and in each session you choose your faction/box to play, for example in a 3 player session each player choose a faction/box.
Each player is expected to bring his/her own faction to the game. (Just like Magic). Like Magic, you can mix the factions to construct your own warband.
Thanks in advance.