I searched for an answer and found this thread: http://stunthanger.com/smf/index.php/topic,21566.0.html, and while it appears that the answer for the color coats is "not much", I didn't get an idea of how much clear and how much thinner.

I'm thinking of just getting a pint each of red, white and blue (or a quart each, if I get Randolph), and as much clear and thinner as you folks tell me I should buy.  Base coat will be white, with blue and red trim.

So -- how much clear, and how much thinner, should I buy to paint a Legacy so that I can be sure that I have enough?  I'll either be painting with Brodak or Randolph -- I understand that it's the same stuff, but I seem to remember that the Randolph dope is thicker, and thus you need less dope and more thinner, so I guess I need to be told by brand.

And, given that I live in Oregon which tends to be wet and cold or hot and dusty (but not, thankfully hot and humid, much), what should I get in the way of retarder to go with the weather?

So how much clear do I need for a whole plane, from the wood up, covering with polyspan?

Randolph
2 quarts clear, one taut, one non-tart
1 quart of white,  will should use less than half, but you will use on other projects
1 gallon of thinner
pints are plenty for trim colors, you can us 1/2 pints or 4oz bottles from Sig or Brodak also.
Smallest pkg for Randolph retarder is quart I think

I generally buy a gallon of non-taunt clear and a gallon of thinner. Goes quite a ways. I buy quarts of base color (white, yellow, whatever) and trim colors in pints. I current have about 40 trim colors under the bench and, I think, 2 quarts of white. Generally, I use a pint+ of clear (unthinned) on bare wood, around a pint to cover and build up base. If I'm using a primer of some sort (mixed clear, talc or zinc sterate or whatever, a bit of white and black to made gray) that's another pint+ or, as I have been doing, just building up with clear. Some sort of blocking coat (if white base color, I usually mix up a bit of light gray for this), Then whatever I need for trim colors. With the white base, if you use very thin blocking coat (maybe a couple of ounces used) then you can shoot on a very thin coat of white and it will cover in one coat (again, usually a couple of ounces + thinner). I haven't used clear dope for top coat in a bit but when I did, it is usually  6-8 coats sprayed and thinner about 50-50 or 60-40. That equates to around 2/3 of a quart of clear and the same of thinner. If done right on a ship the size of your Legacy, you shouldn't add more than 8-10ouces for finish from the wood up. I've gotten decent results and only shot about 6 total ounces worth.

Get a quart of Randolph tautening clear, a gallon of Randolph nontautening clear, and a gallon of thinner: all butyrate.  If Bill Byles tells you different, go by what he says. 

Just before I got to Howard's post I was going to say exactly the same thing.  The clear should stretch for a few airplanes, and since you will be using the butyrate thinner for colors & clear you will likely get a couple of airplanes (maybe three) from that (depending on the in^2 of the project.)

Do what Howard says