You are going USB to connect your panel to your cab?
IMO a swappable approach is best. Make three panels. Each panel can be the width of your cabinet, no need for it to jut out.
1) 2 joysticks with 7 buttons each, or 8 if you like playstation emulation. Build this panel first.
x x x x x x
O x x x O x x x
x x x x
2) a dedicated 4-way joystick, three buttons, and a trackball, for your classic 4-way games, Centipede, Missile Command, etc.
O x x x TB
3) a dedicated Defender joystick, 6 buttons in a Stargate-like layout, a spinner, and a flght stick, for Tron, Defender, Star Trek, Tempest, and so on.
x x
O SP x x FS
x x
But that's my opinion, one of many.