It sounds like you are trying to keep your current stereo, and add on the tablet pc, correct me if I'm wrong. Either way, the disk based version should be fine, tons of people, myself included, run regular spinning disk hard drives in their carputers without issues.
The main concerns with that unit that I would have are :
- The Size of the screen(4.8" is pretty small for a car environment touchscreen)
- Powering it (Cig adapter is the prettiest, or always safest thing)
- How well adapted the software is for mobile use
The major one is the last one, I haven't used android devices much so I don't really know for sure, but if it isn't each to access the music and navigate around in general, it will not only be a major pain but a potential hazard while driving. I'd look into video demos or something and try to decide it if will work for you.
As for the OBD, I haven't used any of those so I can't offer any help there, The keypad should be doable, but I don't know with Android...