I recently had a project that involved painting an airsoft tactical mask in automotive paint to get a metallic finish to some parts of it. I went to a local auto paint shop, browsed their swatches, picked the color I needed (metallic grey, metalic black, and flat white) and they filled aerosol cans in the requested color for me in a couple days. The paints run between $30-40 depending on the color. However since the paint goes on very evenly and only a few coats are needed you have surplus left over for other projects.
To get the best effect, you've got to work it like you would a car that's being painted, that means priming, sanding, the whole nine yards. The real trick to getting an automotive finish though is to use automotive clear coat. Thing is it's expensive to purchase, and I wouldn't recommend trying to do it yourself, unless of course you do that kind of work anyway. I talked with the owner of a local auto body repair shop, and he was willing to clear coat the mask for a very reasonable price, and his turn around was only a few days. The customer was very satisfied with the end result.
As for fusion and acrylic paint, fusion's designed to bond to the surface of plastic, and kind of eliminate the need for primer (tho its still a good idea to use it). If you're putting acrylic over top of the fusion you wont have any problems, nor will you likely have problems putting fusion over acrylic.
the finished mask