looks pretty simple to me, like WR said, buy a cherry keyboard, dremel out the rectangle and proceed to rewire.
i would also cut all the traces with the dremel, like i have in my mods, that would not lead to cross tracing.
and you can wire up any controller as long as it's nice and moddable, ppl here use teensy i guess,
i've repurposed logitech controllers cuz of their awesome pins (i've opened up ms keyboards no pins, razer keyboards no pins, bunch of others laying around no pins).
if you want to use a g15v2 red (the version i've used) i'll gladly provide all the pinouts, i've traced every key. (you just have to understand my logic lol)