So this is something i've been wanting to do for a long time. I'm actually an Apple guy and had been trying to figure out a way to get an iPad mini in the same location but the size of it was just a little to big to fit and operate the way I wanted it too.
So I decided to go with the slightly smaller Nexus 7inch tablet (2013 model) and it worked out perfectly! Along with a Grom bluetooth unit, It has steering wheel controls (volume, next/back, seek) on the music app and pandora/spotify etc.
I also am using an app called Tasker that allows me to automate the tablet to act just like a car stereo. So when I start the car the tablet receives power, it wakes up and locks the screen in the on position, auto connects the bluetooth, and starts playing the song where I left off when I last got out of the car. When I turn car off, it cuts power to the tablet which triggers a custom "Sleep mode" where it will turn the bluetooth off, pause the song, and turn the screen off. It works seamlessly and I love the way it turned out.
Here are some pictures.