There’s nothing wrong with using gloss paints for the finish, and it also eliminates the whole " Apply color coat, Apply Future, Decal, Apply sealer coat, apply Dullcoat" thing… 'Course, I don’t apply Future anyway, since a rattle-can of Testor’s Glosscoat is preferable fro me, since I don’t have to clean an airbrush again, and applying the glosscoat takes twenty seconds…
I apply the color(s), then Glosscoat if I use flats, then the decals, washes (they work best over a gloss finish), then the Dullcoat, then drybrush and pastels (which works best over a flat finsh)…
Going for a weathered finish is probably best done that way… IMHO, you’re on the right track doing so… Unless I plan on heavily chiping paint, like on some Japanese aircraft like my Val here.
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The Val’s paint-chipping is done by using the old rubber cement masking technique over aluminum paint. I painted the green over the aluminum and rubber cement, then when the top coat was dry (not cured though), rubbed off the rubber to expose the “metal” underneath. But that’s another thread…
Fading paint with an airbrush is the next logical step once the “factory” finish is done, and fading is just one of those things that the airbrush was designed to do, lol… A lot of guys like to pre-shade with the airbrush, I’ve never been a fan of that myself, preferring to post-shade with charcoal or pastels instead… It’s quicker, easier, more precise and controlable, and (best of all) correctable if I screw it up…
However, if you want to build Warbirds rather than operational aircraft, then the gloss finish is quite acceptable… You’ll notice the Warbirds at airshows, for instance, are pretty highly polished…
For decal setting solution, I use vinegar… If you decide to do that, rather than a commercial setting solution, always test it on a scrap decal from the sheet you’re gonna use vinegar, since sometimes it needs to be diluted with water a bit… If you haven’t applied a sealer cat over the decals, you can probably get those bad ones off and salvage it
Just one thing you might fix still… The exhaust stacks… Bright silver exhausts, well… Aren’t…
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Not unless it’s a Warbird and the owner the had the stacks chromed after hitting his head while flying inverted… Even brand new stacks on an engine that’s never been fired up will only be a dull stell color…
Heat rusts steel, as you can see on this later-model Spit, and you can start it with the basic rust color (I use Testor’s Rust), then do a little drybrushing with a basic shade of Testor’s Dark Tan, and a bit of “soot” with flat black…
Good luck with your airbrushing… I’ve doing it off and on for about twenty years, and still learn something with every build I do use it on, especially from reading what the other guys in here do… But, I still prefer rattle-cans to the airbrush for simple one, two, & three-color camouflage schemes. Mottling and “squiggles”, like on German aircraft, well… That’s a whole 'nudder animal and one that I really need to practice on, especially German Nightfighters…