I have heard grey primer if you're going to spray the body silver or black, and white primer if you're going to spray any other color. I usually don't use "base coats" unless I'm doing a candy color top coat. Primer, base coats, color coats, clear coats, how many coats are you going to put on a 1/25th scale model? And the more coats, the more build up of paint around your emblems, window trim, etc. or it will cover them up altogether. Use a little paint as you can get away with in achieving your desired results.