How much sprayable single stage paint needed to paint an A body Barracuda? This is a color change so I will paint the jambs, engine compartment, trunk and outer body (I will not paint interior metal of car).

This is my first attempt at spraying a car so I will probably need to error on the conservative side.

5 quarts, 6 quarts, 8 quarts???

when I painted, I bought a gallon of paint, 2 gallons of thinner.

a gallon to a gallon and a half went in the paint. the last half gallon was cleanup.

What color and enamel, laquer, or urethane? Some colors need more coats to cover, and laquer is very thin and will need lots of coats (if you can still find it )

I'm guessing he's going to use single stage polyurethane. This is what I've used so far on my Cuda.

Tip: use a primer that is light in color if your paint is going to be a light color.

The color you decide on makes a difference. Darker colors cover with fewer coats.
I've done color changes on almost every car that I have painted. The A body cars usually take about 3/4 of a gallon of what you refer to as "Sprayable" to cover the engine bay, door jambs and trunk. I've yet to repaint the undersides though. I've sprayed red, black, blue and white. Black covered in 2 coats. Red took 3. My next car will be Detonator Yellow. Its a very "tangy" shade. I'd resurrecting a derelict 74 Duster 360 and the factory GY3 was just too mild for me.

I'm thinking of going with red urethane (Summit brand). I wanted silver but am afraid to try metallic.

Two big factors.....

Are you using a HVLP or old style siphon gun? With The HVLP more material goes on the car and less in the air so less paint is required.

Mixing ratio on the paint is also important. It’s not so much how much paint you buy, but how much sprayable paint you end up with. The ratio of thinner and hardener the paint requires can make a big difference in how far the paint actually goes. I was reminded of this the hard way the last car I painted.....I was trying a different paint and the amount of thinner and hardener required for this particular paint was a lot less than I was used to. I Barely had enough to finish the job.

I’ve been using SS Nason and SS Croma 1urethanes for the last few years and on those you need to cut and buff within 24 hours to get a good finish. If you let it sit longer it tends to haze when you buff it. I suspect the Summit may be the same way.

Just a suggestion but for a first paint job I would suggest maybe trying Nason Acrylic Enamel. It goes on nice and is pretty easy to work with. Like all the old enamels, you can drive it within 24 hours but it needs to cure for 90 days prior to buffing or waxing (the cutting and buffing window is indefinite after that).

Doing this the first time and including jambs, firewall, inside deck lid and hood, probably 6 quarts color plus the required reducer and hardener for a siphon gun (8 if you’re you plan on painting the fenders, doors and hood/deck lid off the car).

When you get the paint mix (especially if you go with Enamel and have it mixed locally) get a bucket and mix all the cans together to make sure you get a uniform color.

it depends on what color and type of paint you are using. sometimes when single stage color formulas are converted over to base coat. if there isn't a formula the mixer just mixes the single stage color then adds 50% more base coat binder to make it base coat color. needless to say you now have a color that has about 75% clear additives and only 25% tints. because of this coverage is rather poor to say the least.
when i do a job like what you are describing i order 2 gallons of paint with a extra empty gallon can. then intermix both gallons together so you have consistent color between the 2. now you won't risk running out of paint and have to order more paint that might not match, due to minor errors when the color is mixed.
the worse thing that can happen is you spend a few extra dollars and probably have some extra paint left over. if that happens get some empty quart or pint cans and pour the extra print in them to save it for another job. if the cans are full and sealed properly it can last a LONG time on the shelf. make sure it doesn't freeze and you will be good to go when you need it again.

Buy 2 gallons to be on safe side ,that way you will have enough to get the job done and some paint leftover in case of a screw up or repair down the road. Use tintable sealer,it will take less paint and less time to paint.

Two gallons of sprayable material,