Stop in for a cup of coffee

Not sure Chris but depending on how well the red covers 1 gallon should be enough but I wouldn't paint the whole truck white first but red then mask off the area for the white stripe and not sure on the size of the stripe but 1 quart should be plenty.
Plan is
Expoxy/Sealer Primer
Dry
2K high build primer
Dry, sand, guide coat etc,
base coat (number of coats as needed
Dry
clear
Dry