On the paint, depends on how carried away you get....If you're like me, and do the inside of the car, bottom of the car, frame, engine, and all the small parts--should plan on 2 gals. sprayable. As for the clear, I've already gone through a gallon, think another one will do it--the clear I'm using is a 4:1 mix ratio and the paint is 1:1.
The fuel tank is a 15 gal RCI unit (part #2161A) that goes in the back with a firewall separating it from the passenger compartment and an external vent... Got this one from Summit for like $210 or so with the sending unit in it.... I'll get a picture of the setup for you one of these first days....