I am doing something like this, but i will be retrofitting a fightstick i own with controller board and Pi.
I am curious about your USB-B power solution. I have ordered a mountable USB-B -> Micro USB to power the Pi. But I am unsure whether the internal cable or aftermarket Usb B cable can support up to 2.4 amps? can you shed som lights on if there are any power issues?
am thinking of upgrading my Pi1 B+ to a Pi3 and it would be a bummer if I need to get new cables.