Intelligent DC DC Converter would be a good supply for the Brix. When you turn on the ignition, it sends a power up pulse to the Brix (2 pin header that you connect to the Brix mobo where it's power switch is connected), then it runs till you turn off the idgnition, when it sends a shutdown pulse and starts a timer to allow the Brix to shutdown gracefully. After a hard timeout that you can set by jumper, it will kill the power so your battery don't drain.
If you use the Driveline front end, and have steering wheel controls and a noise canceling microphone, you can use voice commands and steering wheel buttons for most stuff, then have a small screen in your glove box or somewhere for when you want to see the screen. Alternately, you can get a flip down roof mount monitor, or flip up dash mounted monitor. If you are real handy, you might cut your dash and build a motorized slide up monitor like some caddy's have.