When I do mine, I will sand it with 1000 grit, then primer, then paint. I don't want to have to do it again. I am doing all of my vert trim because it's all faded.
I broke off my drivers side mirror, so I decided to experiment with paint colors on the broken mirror. Semi-gloss black came out great! The regular glossy black didn't match the color of my car at all. And I like the semi-gloss better anyway. If you want it to match, you will need to get your pain code on the b-pillar, and get some that matches. I think you can order some from Pep Boys if I am not mistaken.
Scott