A good buddy who is pretty darn good at finishing says he takes a Pint of clear, cuts it 50/50 making a quart or so.  He applies one coat a day until it is gone.  Usually cutting it up to 60/40 for the final coat or two.  The results are very good.

BIG Bear
RNMM/AMM

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 

Randy,
Spencer Aircraft isn't that far away.  I usually give them a call a couple of weeks before I head
South and tell them what I need.  For colors, they mix it up for me and for clear they make sure they have the A-1619 in stock.  They know me and have it ready when I show up.  They don't charge me in advance and even let me back into the warehouse where they mix colors.  I was looking for some white pigment to add to Insignia White and the guy gave me a quart of the stuff for the cost of a quart of white dope.  Probably enough pigment to mix up 5 to 10 gallons of white.  Hope he didn't get fired   
Alan

Well, it's going to have a catalyzed poly topcoat after all. It was just too humid and hot to successfully use dope. If I had wanted to take the time to experiment with a slower thinner or with retarder, it would probably have worked but I ended up with so many issues with the color then blushing and all manner of apocalypse, I might have taken the time to work it out, but as it is, I just went the easy route.

And Alan, I also get stuff from Spencer but I don't have your panache so they only give me what is in stock. 

Maybe i've been doing it right, but I use just one coat of 2-part automotive "clear-coat".  I doubt if I sprayed more than 1 pint thinned with butyrate thinner.  Full-size stunter with 60" span.  It flows nicely and I couldn't see any need for any more.

Don't try to rub it out.  Rubbing compound has no effect!  Looks the same before and after.

Floyd

Winfred figured a quart of clear, then added a quart of thinner, and sprayed until gone.
He let it gas off thoroughly before he sanded ....finished with Goram's silver polish.
To the best of my knowledge, he never used car paint.......even today, he is painting motorbikes with Brodak lacquers ....I think that he may be using auto clear on the bikes now.
"Tradition" had around 5000 flights, with varying amounts of nitro, and the nose was fine.
Have fun.

Therefore it should be ready for this weekend.