Yes, stay away from 'single stage' metallics. You will not like the outcome, do yourself a favor and do the base/clear like others have suggested. No jams, and a good paint like Duponts Chromabase, or PPG Ditzler line will produce fantastic finishes but are pricey. I am painting my 68 1/2 ton Chevy soon and the materials alone will be over $700 for the paint mentioned above. A good alternative is Nason, Dupont'* econoline. Or Valspar, the House of Color econoline. Also, try NAPA, they carry Martin Senior paints, very good quality too. Top of the line paints are Sikkens, or Glasurit BASF, very expensive but will hold up to years of use and still shine like new (Volvo, Mercedes, Porsche, BMW etc use these as OEM)
Self etching primer is mostly used for bare metal for adhesion, and to bond itself with the metal so the painter has a great place to start his work. I would use a good catylized build primer over the sanded OEM finish, then paint.