If this is just asking what you should buy, then currently for academy there is only the core set and two expansions. Buying one copy of each is definitely enough for one person to build any book they want. If you're supplying two people with cards, there might be some fighting over who gets which card, but I still don't think it'd be that bad.
As for actually building books, both games use the same system, a point buy system, but academy uses fewer points, 40 instead of 120. This results in the books you build being only around half the size (you won't be including as expensive of cards either, so one third points results in one half the number of cards roughly). Overall I'd say this makes building books in academy easier just because of less to work with.
I will add though, that you don't HAVE to have every expansion in either game to enjoy it. Just getting the core set will provide you with ample enjoyment, and then just get expansions as you want them.