Didn't have time to read through everything, so this may be redundant. But here's my suggestions, for whatever it's worth...
1. Maybe get a radon gas check (even if you had one done in the past). Be sure of adequate ventilation. Check for hidden molds or other stuff that can subtly (or not so subtly) affect one's health if breathed in too frequently.
2. I agree with those who advocate for a simple bench and dumbells versus machines or bars, etc. Just a flat, strong, well-padded bench. One that can be raised on an incline can be useful, but not really needed. No need for leg or barbell racks. Long experience has taught me to greatly prefer fixed-weight dumbbells to adjustable ones (no time-wasting with plates and fasteners). A set of fixed-weight dumbbells from very light to more than heavy enough is inexpensive.
3. A set of varying tension resistance bands are great for adding a different type of resistance training that can help fill muscle-group gaps that might otherwise require expensive equipment. There's a practically unlimited set of exercises one can do with bands. For example, a strong-resistance band can provide all the leg-press exercise you'll ever need. And bands can be healthier to use for middle-age and older folks than some other forms of resistance training. If you can mount rings on the walls (at ankle-height, mid-body height, and head-level) helps expand the range of exercises to be done with the bands.
4. I agree with those who mentioned having some sort of static aerobic machine (static bike, treadmill, stair-climber, rower). One or two of those, in combination with bench/dumbbells and resistance bands is probably plenty for basic fitness needs.