Btw, any of you guys watch Ben Heck?
Arduinos have a LOT of shields for them. From GPS shields to SIM card shields that let the arduino connect to a cell phone network. I'd personally ditch the Pi and just use arduinos here, simpler to use with more I/Os. I'd only consider a Pi if I was doing some kind of in dash computer.I seen something like what you're talking about with a wired arduino addon board (shield) and a custom made website app. I don't know if there's a wireless way to do it with the arduino, maybe the raspberry pi.