It's a great shop for sure. Very blessed to have access to it.
The reason I apply clear over each colour is because I'm airbrushing acrylics. They are not very durbale and can easily be scratched off or peeled.
With so much work being doen with frisket masking, I'd have to stick frisket over freshly painted areas to do the next one. It would peel the first colour right off the playfield. If I'm working in areas that are far away from each other, I can do maybe 2 or 3 repairs or colours before shooting some clear. It all depends on the particular playfield.
Once sealed, I sand down each layer so that I don't have a half inch of build-up by the end
The last few coats (once art is done) just get a light scuff sanding to make the next coat grab. The end result is maybe 1/16" of topcoat.
I have a fun project that I did recently on a Stern Cheetah. It requires tons of layering. I'll start posting it today and you can see some of the process.
Also, this old thread of a TAF restore I did has a lot of good info. Not sure why the pics aren't showing, but you can click on the links.
viewtopic.php?f=4&t=129&hilit=taf#p793