1- Why do some cars have a rear diffuser that's tucked up to the body, and others have one that's spaced way down?

2- What do people do for door mechanisms that aren't running outside handles?

3- Is cruise control setup to work with the kit, or do you need to add something to make it work? For reference, I am using a stock ECM and I have no speed sensor on my trans (running GPS for the speedo).

4- Painting body on the chassis or off?

5- Does a rear view mirror do anything in a GTM?

That's it for now. I'm just looking at random GTMs online for motivation.