Signed up just so I could follow this thread!
Can I ask why you changed from a Android box thing to using a mobile device?
I'm looking into doing either with my E30, I can't go over 5" or so screen size if I want the screen in the roof.
You don't happen to know if there are apps that can read data from various inputs around the car? For myself it will really just be from the engine as there isn't much else in the E30 that readings can be taken from.