Now just so everyone understands Goody is just starting with primer. I would think the thinning and method may be a little different for that.
Goody what is your goal with this car right now. Just to get some primer on it so it is one color and won't rust or are you going after a nice smooth surface like Exit1965 got.
If you want smooth and something that is going to last for awhile you need to go get some actual enamel like Primerduster and I used. The flat enamel ends up coming out looking like primer but is going to actually give you some water resistance/durability. Also I don't know about types of primer but that kind you got looks wrong to me. It may still work but just by the name it looks wrong.
If you are not going for that buffed out smooth surface just do your sanding and scuffing with scotch brite pads, maybe use a can of the spray primer for now to hide the steel and then get a gallon of the flat enamel and do the whole car when you are ready.
Todd