I'll throw in my .02 cents. Fender used a sealer before a color to quell the grain. Polyester is the most solid, easy to work with these days. They used "Fullerplast back then. Drop it down, level it out with enough teeth to grab onto the color. I like House Of Color Auto paints. You can get small amounts and spray equiptment cheap to facilitate from auto body and Harbor Freight.
With Laquer when applied to Laquer will meld together very well. The old coat melds with the new coat, so level and re apply. Also Polyester clear is hard, solid and ready for high level wet sanding. End product is very durable and resonant. Go hog wild with color underneath it. The metal flakes and colors are the HOC appeal. Let it all dry out extensively because once you drop Polyester on it is trapped, to avoid strange results.
The polyeurethane stuff to me is gummy and needs more hardener in general. When shooting all in one day you want more time to dry because your spraying a tacky surface. Here your more prone to contaminations, so a clean area to work is key. Your building the 'system' and ending with clear, which you plan to level with 1000 to 2000 wet sand. Buffing wheels generate heat so thats why polyester is so popular and its rock solid resonant/durable. Polyester is also great as a sealer because of being so rock solid and resonant.
I say this because polyester is never going to react to your sweat, heat and it encapsulates the body, like Fender " Fullerplast " did. The Laquers Fender used were thin, and like I mention, additional coats are easy cause they 'meld' easy. The HOC is uber color, especially metal flake. The polyester seals all, can sand out to glass if need be. Add more dry time if you want a more level surface at the expense of picking up contaminants.
Have fun and experiment away. My main deal was reaction to sweat/heat that destroyed the contact area. Fenders age so well because of what I described above. The old Kramers for example were Polyester resin and indestructible. Turns out virutally the same material as Fenders Fullerplast they used as grain sealer. They then applied thin color coats, no clears. So either way, you want Polyester to experiment with, at the very least a grain sealer for max resonance and as a clear, its insane.
I did alot of swirls, dips, color transfers on polyester encapsulated bodies. They never took on water. This process required to 'dunk' the bodies in water for the art processes. Just to give a further testimony for it. When the wood is kiln dried and ready, last thing you want is water or moisture before paint to get 'trapped' inside.
But thats another insight. Velcro Flys pics are increadible, great work and advice with follow up. Just so you guys know where I am coming from. I restore Corvettes and Old Muscle cars with the old paints. Fiberglass flexes and we have systems for that. So with guitars, I want solid , not flex and pliable. I want no reactions with sweat and heat, most of all resonance, but maybe color first with big metal flake too. So thats where polyester kills it. Color sand, and if you want you can buff it on a wheel no problem as long as you pay attention to heat. Thats the red/white compound. Many use Maguires Mirror as a finish. I don't like additives to the paint. Velcro Fly seems to think the same way. Shoot it, let it off gas together and SHINE AWAY. His spray technique is cleary VERY evident, you don't get those results unless you are a pro !, or tutled by one ;-)