QIf I give a Pixie follower in my EX area +1 attack with this spell, then summon that follower, does it keep its +1 attack?

AYes. When an effect is applied to a card in the EX area, that effect will persist even if the card is played or summoned.

QIf I can't select any Pixie followers, can I play this spell?

AYes. "Select up to 2" means you can select 0. Also, if you've played at least 3 cards this turn, you can draw a card even if you don't select any Pixie followers.

QCan I select a Pixie follower from both my field and my EX area?

AYes. You can also select 2 Pixie followers from either your field or your EX area.