As I research more, and think about it, I'm starting to feel that I should buy an Arduino as there are already many people successfully interfacing with their ECU and using LED displays to readout information. It's exactly what I want, and I'm thinking it might even be better overall to leave the Pi with Music and GPS, especially since I'd probably want GPS and
the OBDII data displaying at the same time.
Now to figure out the cheapest way of doing it! Buy an STN1110, or an ELM323, and I need a PCB layout plus what components to buy, etc... ahh the fun of modding.
oxo, I found someone with your username coming up a few times in the Arduino/OBDII discussions