So… if it’s something that’s going to set on a shelf or something like a wh figurine, you don’t need to prime with acrylic or enamel.

If it’s something that’s going the handled (like say, a cosplay prop,) your mileage will vary.

I’d recommend printing off small test parts to see how the paint cures and such. I use small shot-glass-size vase mode prints. (Any one the vases will work, but I suggest anything with more complex contours and a few hard edges.)

Then they get double use as a glue pot when I’m doing glueups with barges cement or similar adhesives (and painting too.)

If you find you do need primer… the stuff I’ve found to work best is rustoleum filler-primer. (Yes. The spray can.) you’ll lose surface details, since it’s designed to fill that in, but makes a wonderful foundation.

Also scuff the surface with a coarse sand paper before you do anything else. This will give whatever base layer you’re using a bit more to bite into.