Tomorrow I'm going to order the various connector components I need. In the near term, I want to just be able to connect the input pins to a breadboard. I recently built a silly circuit that can read out a 6-button Genesis pad and I wanted to hook that up to VF3. I'll reuse the connectors for the more important project: talking to a custom firmware program through the pins.
While you're here, I'm starting to wonder about how hard it would be to get audio into a pair of speakers and also hook up a steering wheel and pedals. What is exposed on the I/O board (or filter board as I understand now it is called)? Do these signals need to be amplified, level-shifted, or impedance matched to typical computer speakers? I know nothing about audio

I think it would be awesome to hook up a PC steering wheel to the game but I imagine that this would require some custom engineering. If the steering wheel and pedals talk over some sort of serial connections and pass down digital data, then it would be pretty easy to build a conversion board. If the Model 3 takes the analog signal directly and has the ADC on-board, then that is a bit trickier but probably not impossible.