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Quantities required vary with the condition of the parts, exactness of surface prep, your spray technique, the "flatness" desired before topcoats and other factors like the shape of the parts being coated. Large flat body panels consume less material per inch covered vs. things like tie rods and small brackets since their surface area precludes catching much of the fan pattern.
That said, two gallons of epoxy primer should do the entire priming and blocking phases of both frame and body. I do not use a seperate build primer in part because it adds another component to possibly fail at a later date. 2 quarts of sprayable material should do the frame and running gear if your technique is good, three otherwise.