You'll probably find all these topics scattered throughout the FFVII forum somewhere if you look closely enough. One on where to level up is on this page, or the second.

For your party - well it really depends who you want. Depending on how you level at the start, most of your characters are capable of anything, so really assign them to do whatever you want. Picking out a specific party for the game is hard, however, because different parts and bosses of the game require different party members. But that aside, I find that I use 2 main parties when I play:

Cloud : Tifa : Barret

Cloud : Barret: Vincent

Take a quick look through the FFVII forum pages and you should find what you want.