starting the car auto is no different than starting the car up manual as far as i can tell...its going through the same process and everything of sending a signal to the ignition and causing the engine to turn over. The heater on thing shouldn't be that much of an issue, the heater core is usually warmed by your cars engine anyways so it heats up as engine heats up. I personally wouldn't leave a car parked for 5-10 minutes with the engine running and heater on just idling though cause you are just wasting gas and getting in it and driving off will warm it up faster i think (my car at least).
$20 kits arent too bad to isntall but definately takes a little knowledge and willingness to look at your cars wiring system and understand how its going to work. you can usually enable/disable auto door locks based on wiring combinations too.