Gold, yellow, white and most metallic colors benefit from a white primer, though in reality any light colour (including grey) will work. This is due to the high light reflective quality, which is why white primer is the best choice. I find that using Tamiya AS-12 Bare Metal Silver also works especially well as a primer. The additional metallic boost would be very nice under the gold.
Even though I have an airbrush, I tend to use rattle cans for metallics as the metallic particles settle very quickly. If you do use an airbrush, give the paint a stir occasionally to keep the particles floating.