First off let me say that this is not in lieu of searching and doing my own research. I am experienced with 12v electronics but know very little about building computers. The budget for my carputer is pretty much whatever it takes to get the job done right, without going overboard. I would prefer to build my own rather than buy a pre-made unit so I'm going to need to familiarize myself with specs/terminology. As of right now I know some key words but a lot of it is a mystery to me.

What I want from my car PC:
-High quality audio signal with frequency tuning capabilities. 2 sets of pre-outs, the higher voltage the better (I will be using a Tru SSLD6 line driver)
-High quality video. I am looking at the CarTFT 7" open frame TMR touch screen.
-OBD2 Scanning. Looking at the ODBPro USB Scantool.
-Engine management via GReddy E-Manage Ultimate
-DC-to-DC power supply

I am planning on using a Fusion Brain to control things like air ride and other accessories.

What I would like as far as operation:
-Quick operation.
-Large storage.
-Ability to perform multiple tasks simultaneously.
-Easy to use and attractive front end.