Have you considered an ibus adapter like the resler one easyrider? It will allow you to use the multifunction steering wheel controls to control the PC without having to take your hand off the wheel. Quite a lot of people use these on BMW CarPCs. You can also do a few other cool things like control pretty much every single electrical component in the car, so for example you could have a button on the screen for any audio function, or even something like the windscreen wipers. You can also read various values from the car like time, speed, miles etc.
Just something else to add into the mix for your future possible upgrades to the system.