I always used Glasurit automotive basecoats since I had access to a paint shop. The Subie crowd is big on headlight masks, and they typically swear by Duplicolor. I used it on some wheels a couple years ago and it has stood up VERY well, but I never personally used it on a light assembly. Granted, you want to do it right the FIRST time, so don't cut any corners. You REALLY don't want to crack the lights open again for a flaw.

Here is what I would suggest:

-Scuff (Scotch-Brite) assembly parts to be painted/ mask off what you don't want painted to protect from scratch marks.

-A few thin coats of self etching prime

-Scuff prime

-Light even coats of base coat. Duplicolor wheel or caliper paint is heat resistant if you are concerned about heat.

Let it dry for a good day before rebaking/sealing. If you want to go the extra distance, fill a bucket with WARM water and drown the assembly lens side up. Keep dunked to look for leaks in the seal. If you don't fix them, you will get fogging in your assembly in some weather conditions.

I imagine you are going with a matte color/base coat? You give the assembly a shiny/lacquer enamel surface, you may get unwanted glare and reflection from the lights.

Above all else, try to have fun and set aside some "grace time", since nothing ever goes right.