Sweet project! As another EE I can really appreciate this
Now... just do this again but with an Apple TV, then take the video output to your head unit as an auxiliary video input device, and it'll show your song information and album art on your dashboard too.
You can use Airfoil (software from Rogue Amoeba) to stream audio to an Airport Express from a Windows or Mac PC.
The doubleTwist app will (apparently) let you do some Airplay streaming from Android devices, but I haven't tried it out.