You write your own software and you know microcontrollers, you're in the same boat as I am. You seem like one of the creative people whose worklogs I love reading. Anyone can do the ordinary but I like that you're screwing with the AC and the remote start.
For the record though, manual remote start isnt a big deal at all, you just need to do a couple checks before you start it. Make sure the parking brake is applied (theres wires already connected to it, look under your center compartment ) and make sure the vehicle is in neutral.
Cant wait to see pics.