Absolute first thing you should do after updating to the latest patch is to run the game with no mods at all and make sure it launches ok and plays. Then when you start putting mods in, if the game doesn't start you know it is the mods and not possibly something with the game or your OS.
Beyond that... Just backup every file you mess with and its hard to make too much of a mess of things.
Edit: Oh yeah, Awwu's ingame trainer has a car spawner in it. Very good tool to have, you can do pretty much anything with that trainer.