I am a little confused. Do you need a car pc to run all of this stuff in your car?
Have you seen http://plxdevices.com
Seems like you just need to hook up there OBDII scanner module and then attach display modules to that and you can make your own custom gauges.
Do you need a separate scanner module for each display? If so, that could get expensive.
This is a project I am interested in doing, but it seems like at this point, there is not a great solution.