Interesting project!
For a start, these guys have been long overdue, and simple
must to find their way into FF7:
That is the "younger" Zack before he became 1st-class, I liked this look better, but either one would be OK.
Aeris and Hojo could probably be picked up too.
I personally didn't like the KH(2) style of heads for everyone, because I felt they were a little too cartoony for the gritty FF7 world.
But please, please, please dont butcher Tifa up!
She may give the impression of a "sex-symbol" to most people, but her design reflects her personality and there is more to her character than just her chest.
In CC, Tifa is 15 (apparantly), so her face and her body should not be used without some modifications.
Hunter's Tifa was OK, but I didn't like it much either (even after replacing the head).
I am a pretty handy modeller too, so if you need any help just PM me and I will try help out.
The CC-File investigation has reached a stable point now with these characters extracted, so I have been thinking of taking on other projects on the side anyway.