I getting ready to sell. The old trim was in very bad shape so I stripped it out, retextured the walls, & repainted. I have been concerned about doing all the trim from scratch since I've never done it before. This looks well within my ability and I agree with your idea of painting everything before installation. In my rentals, with stained molding, I have used trim screws to install all the molding. When it s time to paint, I can pop the trim off, paint without any cutting in and reinstall the trim, It's fast and easy.