I have noticed there are two trades involved in the business of building hot rods, restoring cars that people seem to undervalue and hate to pay any real money for, but they are both time consuming. One is custom hand made upholstery, the other is paint and body work. I've noticed that most people expect to get those services dirt cheap, but they're both time consuming and also require skill.
when i was in high school taking auto tech, we had auto body as well, and the teachers would let the students sit in on each others classes so by the time we graduated auto tech or auto body, we had a good understanding of each skill,and the work involved..the auto body teacher was an old school hot rodder and even taught the kids how to use lead (this was early 90s). one thing i will always remember is him telling us the longer you spend on the prep ,the better the paint will look, especially on black and cars with metal flake (which was popular at that school cause of all the lowriders in the student parking lot)..he also said any idiot can do body work and slap bondo on a car, but a skilled body technician can do magic..and to NEVER rush body work, take the time and do it correctly..
I only guide coat the initial dry sanding, from there it’s fairly easy to tell when you’ve been doing it 45 years. If you’re new to it and guide coat helps, by all means, go for it
we were just talking about that yesterday. The long and short of it is that there is no really good way to do it. I wish I had more of an "ah-ha" answer