Maybe you should look at
http://italianhorses.net/ There is a great tutorial for painting your cars with Tamiya paint. I can also tell you the way I work: Gray primer, white primer. Wait a couple of hours, sand it lightly. Mistcoat of color, thicker layer of coat so you don't see any primer. Let the body dry for 3 to 4 hours and after that clearcoat. If necessary, clearcoating twice directly after eachother is possible also.
Good luck.