Grunt,
From my own experience in prop building, the best type of spray paint to use is automotive. It's relatively inexpensive and very durable. You can handle the piece many times without much wear and tear on the finish. Sealer is key to preventing this.
I would recommend using automotive spray paints for all stages (primer, actual coat, sealer). Using primer allows one to see any imperfections in the piece that need to be fixed/corrected, so apply a couple coats of this to make any final revisions before going on to applying the actual paint.
For the sealer, also referred to as a "clear coat", you can get it in either glossy or matte (flat) finish. Which one you use depends on your personal preference. If you want something with a bright shine use glossy, or if you want a duller metallic shine use matte.
To contend with the humidity, which may cause issues in the paint adhering properly to the piece, best practice is to emmerse the paint in luke-warm water for a few minutes. Warming the paint prior to spraying will allow it to bond to the resin better, and limit any imperfections caused by the coats of paint (that point explained in the following paragraph).
Apply several coats of the base paint, and any additional colours for the details. This should be done slowly, doing a few passes over the piece for each coat. I would strongly suggest against doing each coat in one pass, as that can result in excess paint on the surface of the prop and cause running or "pooling" of paint in certain areas. It's always best to apply a few light layers for each coat. That way you get a much more even and cleaner finish on your prop.
I couldn't say just what colours/paint codes for paint to use, but I hope the above's of some help...
