Let's assume a deck is 40 cards. For some draw-heavy heroes it might be higher (I could see Spiderman going higher), but hero cards are so much better than aspect cards that you're gonna want as much chance to draw them as possible in 95% of decks.
So we start with 15 hero cards. 25 remaining.
Every deck will likely include Energy/Genius/Strength/x2 Power of [aspect]. That's five more cards. Those are cards that will be in every deck, because they provide 2 resources each. You always will have to spend resources over the course of a game, so why not use these and save cards. 20 remaining.
1x Nick Fury will likely be in every deck as well. He is the "Gandalf" of the game, meaning he comes in to bail you out for a turn 95% of LoTR decks have Gandalf, doubt it will be different here. 19 remaining.
So for most decks (let's say 85% in total, given the various assumptions that were made here, it's probably higher though), there are 19 cards to choose. In the core, there seems to be typically 2-3 allies beyond Fury in every deck. So then from there, probably 3x each of 5 different cards, then 1x-2x of one. Of course, there might be some cards that you only want one or two of, so I mean it could be a lot more complicated than that, but still, the theory holds.
So it looks like, including allies, and allowing for some 1x and 2x cards, you'll be choosing 10 different card titles to put in your deck.
Thoughts?