Alittle late to bring this up. But you don't need 7 buttons for Player 3 & 4.
Actually, I only have 6 for 3 & 4. The reason I have that many is this will be a console machine. The reason I have it that way is for games like Tekken Tag, DOA, etc. Also, I layed it out so that 3 button games (NBA Jam, NFL Blitz) would feel right, as well as fighters like Tekken would feel right. Plus it has the traditional Neo Geo layout (don't know if there are any 4 player Neo Geo games, but figured what the heck).