The description of taking off the popcorn stuff on the upper wall and ceiling matches what my sister described doing at her house in Seattle. Hers is plaster and is sheetrock, but the spraying with a garden sprayer and scraping it off carefully sounds the same. Another thought I've had is to simply remove the ceiling and put in boards (tongue and groove) Here is an example. I don't know if I'd leave it wood or paint it (whichever the case, it would be stained or painted board by board before they're put up).

Thanks for the update, Rapaire. I have a craft sunroom here that I designed in when I remodeled the house, and I love it. It's where "works in progress" can stay out for a while and not be disturbed before they're ready. I reorganized my shelving last year (a large shallow cupboard with a pair of mirrored closet doors that slide across the front of it) and it's much easier to work on things now. The bits are all nearby.

SRS