The best primer for acyrlic paint is a clean plastic surface—much cleaner than you may be used to. Enamels contain solvents that will dissolve small amounts of skin oil left on the surface—acrylics don't. Cleaning with a surfactant cleaner, followed by a distilled or deionized water rinse, then an alcohol wipe should leave a pristine surface.
I use Tamiya grays as primers. Using an enamel primer is fine, as long as you don't overcoat with acylic until the enamel is fully cured.