Filler and painting on '98 S70 Rocker Panel trim covers

[LowEnergyParticle]

My 1998 S70's right-hand plastic rocker panel trim cover took a hit from a curb that came to life, leaped out, and knocked the daylights out of the cover. Bad luck all around.

I ordered a replacement from myvolvopartsonline along with 8 oz of spray can paint and 8 oz of spray pan clear laquer. I've got two questions, if that's OK:

1) The new plastic trim cover has a small nick in a very visible place. I'd like to sand it down and fill it, but I don't know what kind of filler to use on a plastic part like this. What kind of filler works well on plastic?

2) The trim cover is already primed on the outside. What is a good sequence to do the paint work in? Sanding in-between coats? What grit? How many coats of clear laquer, and how long do you wait in between? Sorry for the very basic questions; I have never painted an automobile part before.

Thanks very much!
Dave