If you don't want SF specifically, you don't need six buttons. Neo-Geo games seem to need four buttons.
If you like the old games, you might consider arranging your buttons like my first cab. I have only one player, with four buttons. They are arranged in a square and allow me to play QBert with buttons instead of a joystick. Unless you come up with some wierd scheme (a dedicated joy that's rotated), that game is not very good in most MAME cabs. With four buttons in a square, you can control the direction by pushing the buttons. Works great!