One additional thought on "how much". George Kirby should not be confused with his buddy Benjamin Moore! Kirby mixes his paint in very small batches and so there will some minor color variation from cans purchased at different times. Usually not a problem if you are recoating the entire canoe. If you run out partway down and start with a can from a different batch, you might see a difference.
On my new 16' Chestnut Pal I applied four coats of Kirby's paint, without thinning, using one quart of paint with just a bit left over. Prior to this, I has applied and sanded two coats of Epifane's primer.
I used kirby primer under kirby paint as I recall. I believe the Kirby conditioner would be better than plain penetrol. I have used a little thinner and a little penetrol in the Kirby paint. I've also used TSC tractor paint at less than $10.00 quart with thinner and penetrol.
Here's my advice. Do whatever McDaniel is doing. you should see his paint work.
I use a primer as well,l for the same reasons Dave mentioned: fills better, sands easier, costs less. I use Interlux PreCoat (which contains microballons), but usually recommended the manufacturers recommended primer just to be safe. That's one area where you can mix systems safely, unless you're using some exotic top coat, which Kirby isn't. I reduce my finish paint with no more than 10% thinner, again as recommended by the manufacturer. In my case, that has always been the 333 thinner in the Interlux one part paints. I believe it's the 121 in the Pettit. Penetrol works as well, as does plain old mineral spirits, found in all of them. Now that I've escaped the corporate world and am free to experiment publicly a little more. I'm going to do so, but will start by following the manufacturers recommendations, modifying from there.