Best paint, best primer, and best sealer are a matter of opinion, but many here use Createx paints. For sealer, probably the two most common are Devcon2 which is an expoxy glue available at Walmart, and Envirotex, which is also widely available.
I paint with enamels so others will be better able to advise you on where to find the best deals on Createx paints. If you look on this board you'll notice some fine work done with Createx.
There are different primers available for wood and plastic. I believe Krylon makes a primer designed specifically for plastics. I can't think of the name of it right now, but I use it for both wood and plastic and have had good luck with it.