Take Me To Paint School!

Im no paint expert by any means but one thing I can tell you is you want to use a good 2K epoxy primer on bare steel. Keep in mind that most epoxys are not sandable so its best to follow up with some high build within the recoat time specified for the epoxy. If not it can be a real ***** to scuff.
As far as I know you can put just about anything over epoxy without any problems. Just be sure to download spec sheets and read up prior to buying anything.
Harbor freight makes decent hvlp guns if your just doing small stuff. I wouldnt try shooting a whole car with one other than maybe primer.