If I'm reading the Modular Abilities entry correctly, you can have a different set of skills available for each animal, but the total amount of Refresh you'd have to pay would only be for whichever form costs the MOST Refresh, plus 2. So if you wanted, say, a killer whale in the mix, that'd be Aquatic (-1), Claws (teeth) (-1), Hulking Size (-2), Inhuman Strength (-2), for a total of -6, minus two more for a -8 total, and then True Shapeshifting is -4, +1 for human form...
So that'd be -11 you'd need altogether (no easy task; I'd weaken your whale form to a dolphin or something :-P ), but you wouldn't need any MORE than that to put together a bunch of other forms, provided the total Refresh for the powers of each form are -6 or less.
Again, that's if I'm reading the Modular Abilities power correctly. Someone correct me if I'm wrong.