looks a nice install.
If you use a reletively new android tablet, you can run an app called 'tasker' which when the external power supply is lost, will automatically put the tablet into aeroplane mode, turn screen off etc.
Then when power is resumed it can enable GPS and data, and start any apps you want.
Makes for nice quick startup times.

Have a read of this
http://www.rx7club.com/adaptronic-en...-more-1037541/

You won't need the ecu interface bit, but the audio output is pretty good.