Nice look! Did you hear the circuit called "I-Pac" from http://www.ultimarc.com
? It's a circuit that emulate some buttons and you can plug it into the usb. I had build in the past an old Mame arcade cab, that i dont have anymore. This with some Mamewah menu design layout interface frontend.
If you would like to look at some old circuit of a control board ive made in the past, then you can take a look at: http://sylvain.heliohost.org/arcade
. Its really not much there. I simply show some youtube videos of how i have made some old arcade control board, with some real arcade buttons and joysticks. There is also some old pdf document plan of the holes in the wood, the distances betweens the holes; briefly you can see an old arcade control board ive made in the past. It is made with the circuit "I-pac 4".
You will see there is a lot of buttons. But this is because the buttons are close beside the others buttons. Also that there are Mame arcade games that use 1 joystick and 2 horizontals lines of 4 buttons, beside the quarter coins and start buttons. Also there is arcade games that required to play only 2 joysticks. I have made in the past a Mame arcade control board compatible with all Mame Arcade Games (except shooting games, because it's not a lightgun).
Well i hope it will help your self in your creation?