7" Screen fits fine in most Double DIN opening, 8" however do not, they are taller than a 8" screen and will require customization. If your after the OEM look (less chances of thief), then get a good screen (Xenarc is fine) and get a fascia from Bybyte, Double DIN kit
That should set you up for your primary monitor
The video card you won't need, but you need to ask yourself just what you'll be watching.
I'm not sure about these Atom powered boards ability to do OTA HD content (720p/1080i) and the switch over is in less than 90 days. I opted from my HTPC experience to go with a proven setup I know will accelerated any video codec out there.
You might want to look deeper into that.
Otherwise sounds like a good setup...