Alex,
I use automotive acrylic all the time, with fantastic results. The paint dries extremely quickly, and lays down very well to a thickness far less that the thickness applied. You have to be careful, as it has "hot" thinners that can etch styrene, and in the worst cases, if you apply the paint too thickly, it can warp or slightly melt thin section parts such as car bodies.
I sometimes use a clear topcoat over automotive acrylic paint, but you must never, ever apply automotive acrylic over any other type of paint. I can almost guarantee you'll kill the underlying paint every time.
I use a good quality primer with "general purpose" thinners. I tend to use spray cans, using a short length drinking straw to spray the paint into my airbrush jar.
Spray cans are convenient, and you can get "touch up" cans in almost any color that a car has been painted. I use a high quality thinner for the color coats. Always think of the final color before you start priming - using a white primer for reds, yellows, or other lighter colors means you have to apply less paint to obtain a full, deep color. Using a gray primer under white means you have to apply more white paint to cover the gray.
You'll need to thin the paint a fair amount. Lightly dust on a few coats of primer, allowing drying time of ten minutes or so between coats. If the primer coat is fine, then lightly dust on a color coat. Allow 30 minutes or so, hit it with another color coat, then a good wet coat. Allowing drying time between all the coats means that you're kind of providing a barrier between the plastic and the next coat of paint.
One great thing about the quick drying, is that you can rub off specks of dust in between coats.
Once you have the required thickness of paint, allow 2 or 3 days to dry and then rub the paint back with at least 2000 wet or dry. Allow another day to dry (allowing the un-evaporated thinners to escape from under the surface). Then you can polish it with real auto polish - I use Meguair's yellow wax - fantastic stuff - but it's expensive. A full size bottle should last for half of forever. Watch out for high spots like ridges and panel edges - it's easy to polish through the paint into the undercoat.
Using this technique I can get a flawless, perfect gloss, with the advantage of an extremely thin coat of paint.
If you try it out and have problems, or if you have any more questions, you can always email me at the link below.
Cheers,
LeeTree