Others will chime in on the technical aspects of painting, but I can tell you that you'll be glad that you removed both the bottom bracket bearing and the headset cups. It's less to mask, the results will be cleaner.
Painting a frame is an expensive proposition. I've done it and gotten reasonable results. I'm doing another frame over this winter and spring. Meticulous prep work is what you'll need. There are folks on this forum who are experts, they can advise on materials.