viper red is super high solids pigment, meaning it covers great. personally i would put it over white sealer. a gallon of base, i assume not reduced, will be plenty, but you can always get more just in case.
i like lots of clear, cuz i REALLY love colorsanding and polishing
a gallon will go about 3 good coats on everything, i guess if you need "more" is up to you.