Okay, the heat has passed, time to get back to work. I sanded the primer today with a combination of the fine side of the sanding sponge and the "0000" steel wool, but mostly the steel wool. There were a couple of rough spots in the primer on the frame, which smoothed out nicely with a very light application of the sanding sponge. The key is a very light touch, basically don't apply any pressure at all--the result is more like buffing than sanding. As near as I can tell, the goal is just to take a bit of the dullness out of the primer coat, to smooth it out so the paint has a nice, smooth surface to adhere to.
Maybe I'll start the paint in a day or two, but in the meantime I have to do actual work. Also, I'm really nervous that I'm going to screw up the paint royally, so I'm waiting for just the right time. And then screw it up.