I would use a 2k urethane primer.PPG also has a primer called DP40 or dupont variprime all excelent primers.As far as topcoat a synthetic enamel wont last as long as a acrylic enamel.A urethane enamel would last the longest.Consider the color you will use.If using a red the cheaper enamels will "chalk out" a lot sooner than the better ones.Red is by far the most expensive paints(at least in automotive paint)as it has the most pigment than all other colors.But like i said it will chalk out relitively fast the cheaper paint that you use