Here you go
http://www.makemymodel.com/catalog/painting_finishing.php
Step 1 can take hours. :-[
You also risk removing nearby detail that you did not want to remove. I nearly obliterated the lug bolts on the front wheels on this KW T800 when I was sanding the fenders.
And, it is hard to tell if you have it sanded it enough until you paint it. I airbrushed this KW with primer, and then stripped it and sanded some more. I have airbrushed my school bus twice, but I need to strip it again and do some more sanding.
I agree with Catt's suggestion that having separate chassis and bodies (like the school bus) would aid in preparing the model for painting.
Nevertheless, I am glad Make My Model is attempting to fill some of the N scale vehicle voids we have. However, I would not like to have to build a whole fleet of trucks using their models. The pewter kits from GHQ, Showcase Miniatures and C in C are much easier to finish, and they have better detail.
Carter