Cool project! I started something like it a few years ago, but didn’t have a raspberry pi at the time.
For the sake of portability (and because I haven’t mucked around with the GPIO pins on the pi yet), I would wire it up to another controller with a USB on it. Something like this, though I can’t confirm its compatibility with the pi: http://www.diyarcade.com/usb-arcade-control-encoder
That way, if you get frustrated or bored with using the raspberry pi, you can just plug the USB into another machine without having to completely rewire. From there it would just be a matter of plugging it in and configuring your emulators to recognise the buttons.
I ended up wiring my arcade buttons up to the PCB of an old wired Xbox 360 controller as an obsession with street fighter 4 took hold. This is a pain in the arse, and I would not wish it upon anyone.
I’m having trouble. first of all, retro pi image 2.3 is taking foooorever to download.I downloaded the torrent and successfully was able to get the file after a virus outbreak on my laptop thanks to bitcommet. copied to my sd card, plugged everything in to the raspberry and booted but no image appeared. just downloaded the beta image for retropie. my questions are, can I first boot using a wifi adapter or does it have to be with an Ethernet cable?
also I have ps3 knockoff wireless controller, will it work? replies would greatly help thank you