Hi Tom...You always, if you can, shoot flat, especially if there are different colors. It comes from the old Lacquer days. If you intend to have a final product with a semi or gloss Clear Coat its much easier to shoot flat than gloss over gloss over gloss. Adhesion is better also. You are not roughing up your gloss under layer to shoot another color coat over it. And I always shoot a clear coat even if it is satin to protect the paint and the graphics even if I am shooting stencils. The clear coats these days are incredibly tough and resist hangar rash very well. When you shoot a project like the one in your picture with flat you are scratching, touching, marring the actual pigments of the paints...in your case if you were to put a satin clear coat over your end result, you would be amazed at how tough the surface would be to resist fingerprints, hangar rash, even flight rash. And remember my Sukhoi will have smoke on it...so protecting the details like screws and rivets...panel lines etc. from the oil residue mandates a clear coat. So that's why Flat first, Clear second.
Rick