I've painted several hundred figures for the layout, both metal and plastic. I've always given them a light coat of primer first - rattle cans are just fine. Something an expert painter of military figures taught me: prime in black. With black undercoat gaps in covering paint show as shadow, or detail.
I use acrylic artist colors, Liquitex or similar. Coverage is excellent, and the range of colors available is immense. I generally use matt liquid colors, but gloss is fine, just use a bit of matte spray to finish the job.