I won't be painting the door jambs, engine compartment or trunk but I do need to paint the underside of the replacement hood and a set of wheels. Going to use a polyurethane base/clear in the original GB2 light blue metallic.
Anybody?

Hard to say, the quality of the paint makes a difference. I painted F4 green on my dart and it covered on the first coat. I painted some parts F6 green and it didn't cover until the third coat. What color is the primer? This can affect the coverage also. Your gun can waist paint too. Is it a HVLP?

If you are painting the whole car I would buy a gallon. It would leave you with extra paint that would be the best chance of ever matching in the event you have to repaint some area. Light blue metalic is a tough color to match. If it were mine I would make a note of the mix ratio and air pressure you used and toss it in the glovebox for future reference and hope you never need it.

I used a gallon and a half sprayable, so we prolly only mixed up half that. A full gallon of material should do it, Reduced I used most the gallon and a half, but I sprayed Pink, so we took care to get a good cover the first time with no issues.

Depends on brand/mix ratio, some are 4 to 1, others 1 to 1. Also for me to buy say 3 quarts, usually a gallon is about the same price... better to have extra than not enough.

Thanks to all who replied so far.
Yes, I'm aware there is sprayable volume and pre-reduced volume. I didn't want to be too specific in my questions and potentially limit the replies. I did price paint at one independent local store and it came to over $900 for a gallon of base and all the other chemicals needed. When I said that was a little more than I expected the salesperson re-ran the price using 2 quarts of base, saying it would probably be enough. This stuff is expensive and I don't want a ton left over to dry out on a shelf. And I certainly don't want to run out. The price was for a Valspar base/clear polyurethane with a tinted primer and related materials and using the mid-priced clear. There are a several places around that sell Omni but I haven't priced it yet. Opinions encouraged.

Most lower line paints have less pigment per volume than the higher ends paints so I usually price materials both ways. Depending on color sometimes there's mot that much difference considering the amount you have to buy.There's usually more info available on the higher end base such as whether they recommend a tinted sealer which helps coverage and distance materials. Alot of times it's hard to nail a paint counter person on how much materials you need as some don't have any painting experience.

While i probably haven't painted your color with base/clear I can't tell you how fast it covers. I painted my 69 rr f3 light green and it covered very well over gray primer. If you are painting the entire car less door jambs and engine compartment they recommend 2 coats. I doubt you could do it with 2 quarts. As someone said usually where i get my paint it is the same price whether you buy 3 qts. or a gallon. Paint prices are really crazy these days. In my experience the best clear you can afford is well worth the money. Is the basecoat where the high cost comes from?