If I was going to use silver as a barrier, that's the way I would do it. A light coat of primer to prepare the plastic for paint, then your coat of silver. At that point, you can paint your body colour over the silver, or another light coat of primer over the silver first, then paint. Depending on how smooth everything is, you may want to do some light sanding of the silver/primer before laying down the final colour.
However, if you are worried about paint build-up, you could probably get away with no primer at all. Paint your silver over the bare plastic, then your colour. Something to keep in mind; If you are doing any masking, sometimes the tape can pull the colour coat off the silver base. It might be best to test on scrap plastic first, before committing to your project. Also, be sure all coats are well cured before advancing to the next step.
...or, you can paint with acrylic, which should not experience bleeding. I'm not aware of any good hobby acrylics in a spray can, though, and some non-hobby paints labelled as acrylics can still be hot enough to promote bleeding.