Reply to Wooden suitcase gamepad arcade DIY Project

Hello, I have been wanting a midi fighter looking controller with a couple of faders and some knobs since I saw Ean upload a vid about his custom midi fighter. Now a couple of days ago I saw fbonito's midi controller made out of a old wooden suitcase, weird enough I found a very simular looking stuffed in the back of a closet...
It opens in the "door seller way" but I don't feel like changing the way it opens incase I might break it . I have a couple of ps2 controllers with joysticks that I might wanna use. But is it a problem using two of the same controlers with a usb to 2x ps2 converter? Should I pick up some buzz controllers instead? and use them with a single ps2 controller would that remove the problem of the signals being duplicated?

Also, how many buttons and knobs / sliders would I be able to add with a ps2 controller? And where do I wire the buttons? (I havent cut of the thin green button layer off)

for buttons I wanna use arcade buttons or monome buttons like thise http://www.sparkfun.com/products/7835 but then Id have to have leds and it would be alot more complicated..

Yes its my first DIY project

I have a guitar hero guitar here somewhere too, but I assume its less buttons then a regular ps2 controller.