Geez Randy, Couldn't find anyone in the PNW to answer your question? Let's see, Paul, Chris, Pete, myself and a few others. The number of coats depends on two things. How smooth is your base and how much are you thinning your clear. I'm of the starting with a few heavy coats (40% clear/60% thinner) discipline. This is to bury trim lines and decorations. After I get all that covered I start reducing the mix and spraying the whole airplane. This can go on for 5 to 8 coats with a little further reduction with each coat. My last couple of coats are probably only 15% clear and 85% thinner. Sanding of coats starts after the trim is buried. I usually start with 3M 800 grit at that point. My last sanding before my final coat of clear is usually done with 1500 grit. Your final weight increase on a 650 sq. in. plane should only add between 2.5 to 3 oz.
I use Randolph A-1619 non-tautening clear. As to automotive clear, I have only used it once and will leave it for auto finishers. In a word, it's heavy. I went from a model that should have ended up weighing around 64 oz. ready to go to a model that weighed 72 oz. It flew ok, but was not happy. Hey besides, electrons don't affect your finish.
Alan