How hard would it be to write an app that controls the AC?

 

Very difficult.
And this is coming from someone that writes apk's.
I cannot, however, speak on Apple OS. Just from a Android OS perspective.

 

If you get an Android tablet, you can use Google maps offline. Just need to download your area. https://support.google.com/gmm/bin/a...answer=2650218

I recommended getting the Nexus 7 rather than an ipad mini. For $199, you get more of the latest tech for less money than the mini.
http://www.google.com/nexus/7/

 

^ I agree. iOS < aOS

 

Not to mention your iPad would have to be hardwired to the car's interface that controls the AC etc. Otherwise how else could you control it even if you had the app.

 

I did it in my RX330:

 

I redid mine from an Ipad 2 to this 10.1 Samsung