Add new player

Hi, i started to play in solo mode, to test it, clarify rule, and be fluent with the game.

Now i want to add a new player (my wife) to play with me but i didn't find any information about choosing mask for new player. Is it like in the tutorial, choosing 2 cards from masks in the pool ?

Another question about players, why in the rule it's not recommanded to continue the campaign by starting a new dream, without the full team ? for exemple, my wife will not want to play all the dreams, so i would like to be flexible, to play the campaign, in solo or two player when i want.

What do you think about it ?