This first post will act as a placeholder, final result post, and a materials manifest for this modification.

The problem: I would like to retrofit my vehicle with functional navigation, back up camera, movie function, handsfree telephony, and internet functions.

The bumps along the way:

1. Android tablets which support AV-IN, lack bluetooth, or are horribly outdated.
2. My E53 feeds power to everything constantly. This will have to change.
3. Would be nice to hear the phone over the car's audio. This is a bump because tablet bluetooth telephony allows phone control, but not audio stream AFAIK.
4. Easy to maintain (as little variables as possible)
5. Double DIN tablets (premade solutions) look nasty. I'm not a rapper from Miami either to ride with something flashy like that.

The Solution:
Move the current unit to ash tray like StrayS2K. Install Aux cable. Install Windows tablet. Change car options to turn off always-on interior power. Ensure double DIN is accessible for turning on and off tablet, in case it is to ever die while "sleeping". Install rear camera, wire to Easycap, wire easycap to tablet.