Two-Tone Layering Question

Acrylic enamel is a single stage. An ancient, non hardened (although some brands can be hardened) low uv resistance single stage. That said it was the industry standard for a long time.
Enamel also takes a long time to dry. You'll have to apply the second color days later (maybe less consult the tecnical data from the manufacturer).

A urethane single stage like you mentioned in the first post, while more expensive, will have better fade resistance and cure much faster. Things to know ahead of time: Paint, even solid color, has pigment settling, so you can only do the barest minimum wet sanding an buffing. If you have a run or sag you may see an impression or outline even when sanded flat and buffed back to a gloss. Using single stage the line between colors will always be apparent.

As far as the holes, if they are about 1/4" or smaller you can mig them closed easy. A tack at a time until you have it filled in you'll be done before you know it. There will be some grinding involved, but if you keep the heat at a reasonable level there shouldn't be much warping. Once you're done some metal etch primer and undercoating on the backside will keep it from going bad for a long time.

Edit: re-read your post. You can disregard most of what I said above about paint as it won't apply to what you're looking at(I think, going over to tcp global to check it out). if it's not single stage, then its base coat for a base/clear system. you really have to clear coat over it or it will go bad, fade and chalk up quickly.