About vehicles:
No clue, my guess is that the FPSC program has it hard coded that the player is going to be controlling his model and not another entity (like a car).
About multiple levels:
I do believe the program tells you how to do it, if not they would have a video tutorial on it on their site in the "File" section, but for the sake of being helpful, here's how you do it.
Step #1: Make a level.
Step #2: Make another level.
Step #3: Go to File->Build Game
Step #4: In the dialog box that comes up go to the "Level Settings" tab
Step #5: In that tab you will see a section about levels and level numbers, this is where you tell the Editor what level files you want to be what level number.
There ya go, that's a crash course on multiple levels. Hope it helped you out some.
The one and only,
~PlystirE~
In Soviet Russia, road forks you!
Mom: I may not be the alpha and omega, but I can sure as hell be yours!