1. If you can, move away from a laptop board, however if it's easier for version 1. go with it, but for the final version you will probably use a Mini ITX ot MATX board.
2. Audio maybe? Also an on/off switch, mouse JIC
3. The 7" Screens should fit fine in the X5, check out mybimmer.net for a suitable bezel. Xenarc/Gain are better quality, Lilliputs used to be flakey but it is said the newer ones are better. Also look at linitx if you are UK based.
4. Blind Stag
5. Fans or don't let excess heat get in there in hte first place
6. What's the question?
7. Most versatile and cheapest Road Runner, easiest to setup Centrafuse or FreeICE.
8. Reslers, he does Serial or USB.