some people have used cloud from kingdom hearts 2 (and he looks llike the one from advent children) although i severely doubt you'll get the models to the same quality as the ones in the film LMAO
You dont need even a 1M-polygon-model for FF7 rofl

btw, not only the AC model but also any kinds are possible to be taken in FF7 if you know the basic of FF7's data. Believe me, it wouldnt take such long time to understand