To be a bit more precise the marking on the back of the windshield trim is >UP-GF-30< My understanding of that is UP = Unsaturated polyester resin, with reinforcement of GF= Glass Fiber and the final 30 I believe indicates a nitrogen based fire retardant. So it is a thermo plastic and as such will require a first coat adhesive primer if you remove all previous coatings and get to the base material. It may be easier to sand it until smooth by not removing all previous coatings, and then use a standard filler sandable primer before your new color coat.
On the windshield trim you may want to consider a single stage paint vice the OEM color coat and then a clear coat. The single stage one coat paint is both a color coat and clear coat. Single stage paints do not dry as hard as the two step process, thus they will not get as hard or as brittle as the OEM paint. The windshield trim takes a lot of abuse as to road dirt and bugs hitting it and I prefer the more malleable single stage paints for this use as they will not chip as easily as the two step color coat and clear.