With my rig I couldn't do a coin door, so i have coin buttons next to each players start button.
My trackball came with 3 mouse inputs. I first tried to use those for esc, pause, and enter (select game, pause game, exit game) but ran into issues using them with maximus. So Later I hooked those 3 buttons into my ipac to make it easier to set those buttons within maximus arcade.
Those 3 buttons imo are useful because it makes it extemely easy for my kids and friends to negotiate the fe menus without having to be a rocket scientist,
Then I have 'hidden' controls utilizing the shift key feature with the ipac on player one. With these I can bring up mame menu's and change individual games or settings etc.