I have had my seats re-upholstered in a light dove grey ultra leather. My seats originally came out of a vehicle and all the trim pieces are tan colored. I have never painted much of anything let alone plastic trim. Just exactly what is the procedure that needs to be done so the trim will come out looking "show quality" like my seats & interior?

Do the trim pieces need to be washed with detergent to remove grease/wax or use a wax & grease remover? Does the aforementioned need to be done prior to sanding or just prior to painting? I am not sure if all the sanding will remove all the wax & grease which may have gotten down inside the plastic?

What grit of sand paper needs to be used from beginning to end of the sanding prior to priming? I'm wondering how much work it will be to make sure the tan color of the original trim pieces does not bleed through the light grey paint which will be used on the trim pieces? The trim pieces have been lightly scratched in a couple places and I need to make sure they look absolutely PERFECT prior to painting so the outcome will be top notch. Does it take a SPECIAL type of paint and primer for painting plastic? Thanks for the advice.