Would I be allowed to double up on sets in draft?
I think the Official Guide just says "available" booster packs, so if you have more of one type and none of another, doubling up on one would be fine. The main thing is that you need enough packs to make a deck of at least 50 cards, and several cards that are drafted will not be usable. Also keep in mind that the blue and green packs have less cards than the others.
Just make sure the players know what packs you are using, since they are paying extra for the category. I know I wouldn't pay $10 to play a Booster Draft of 7 blue packs.
