The paint will get a better grip on the surface if you do a light sand and primer.
I would use an 800 grit wet sandpaper to lightly rought the surface and them use auto primer from the same brand of paints you plan to use.
Be carefull as some primers do not work with some paints. (I learned that the hard way on a Vader helmet.)
And several light coats is better that a big messy run in the paint.