The best YouTube videos about finishing drywall are made by the professionals. But you have to keep in mind, to make a living at it, they have to work quickly, do as little sanding as possible, and build up arm muscles.
I discovered you can skim coat in sections as long as you don't overlap the sections until they are completely dry. Doing it that way just means it takes extra time and you may have to do more sanding. That doesn't matter to me for a one-time job.
Last night I went around the edges of the ceiling in disjoint sections as large as possible until either the "mud" got too dry, or my arm gave out. Then worked out from the middle. Today I'll try to fill in the missed sections. It may take a 3rd day.
This morning the ceiling is looking so good already, I'm starting to rethink doing wallpaper. Just finish the walls and paint them also. There is some really bad damage around the top of the shower, but I might be able to fix it and paint in the same amount of time it would take to put up wallpaper.
While I'm at it, I could rewire the electric circuit that room is on and add some outlets or light fixtures above the sink. That circuit is the only one left in the house that is not grounded. The dining room has surface wiring and you hardly notice it because it's painted the same color as the walls and ceiling. It suits an old house. Surface wiring would be hard to do over wallpaper.