Many of the artist-type acrylics are primarily for porous surfaces such as paper or cloth, others adhere well to plastic. It just depends on the specific acrylic paint you are referring to. If it is indicated for use on plastic it "Should" be OK but I would recommend trying it on some scrap first.
Acrylics take some getting used to. They don't adhere as well as enamel or laquer and they dry so fast that even that can be a problem. It is important that the surface be clean of oil and grease before painting, and if you have to mask over the acrylic use either low-tack masking tape or a coat of enamel primer under the acrylic. They tend to pull loose quite easily if you aren't careful.
It isn't usually necessary to apply a clear coat afterwards. Acrylic is pretty tough. If your paint dries flat I'd recommend a clear gloss coat prior to decaling or your decals will develop a bad case of "Silvering" because of the air trapped beneath the decal in the texture of the flat paint. Most of us use Future floor polish for that. It's a clear acrylic that can be airbrushed or hand brushed and works quite well as a barrier coat or as a final gloss coat.