How much of a setup/tear down is acceptable?
For example, how often would it need to accomdate guests?
My darkroom is in our spare bathroom. I've installed a counter over the toilet (at the end-wall of the room) joined at right angles to another that fits over the tub. These support the Enlarger and associated stuff, and trays and/or my Nova. The sink is open which is where I do the film processing. On a day to day basis the room is no longer functional as a bathroom, but it all could be taken down in a few hours if necessary, the only permanent changes I've made so far was the sink and vanity which now is a narrow counter supporting a single bowl stainless kitchen sink, with temperature controlled water. Plywood covers the window to make it light tight.
At some point I plan to remove the toilet and probably the bathtub, but for now they are still in place and functional.