I fit a 2-player arrangement into a 8"x24.5" panel. 2 sticks and six player buttons each plus a row along the top for coin1/2, 1P/2P start, pause, and escape.
My microswitches extend vertically so there's space (although it's tight underneath).
Not alot of palm-rest space, but it's compact, clean looking, and uncluttered.
Make a mock-up out of plywood or MDF to try it out.