I don't understand the FF7 engine exactly, but I stuck a 6000 poly nurms subdivided head in there and it ran fine. You really don't need to be to fussy when your modeling for this engine, so making a high poly mesh first, then I'm assuming you would mean do a normal map afterwards. I reckon it would be unnecessary.
So you can basically add as much detail as you want texture as large as you want, and use whatever method of modeling you feel necessary, and this engine will just suck it up. It really baffles me as to how this works but, yeah I've tried quite a few different things.