Hiker, you are a gem. I am awed by your discipline and methodical way in which you did all this. The amount of willpower you have must be amazing. Were you an athlete perchance?

Did the L5 issue resolve, do you think it was worsening your neck pain and shoulder pain. Any exercises that helped there? I think I have a herniated disc on the left side thanks to a stupid mobilization by an arrogant PT who was into manual therapy. As a result, I have developed twisting in the lower back too.

Another thing, I learnt abdominal crunches are pretty bad for folks with kyphotic posture as they strengthen the rectus abdominis that basically pulls down on the rib cage and hunches one over. Another exercise most folks benefit from (supposedly) is the heel slide. Basically lie on your back, and making sure hips dont move, back is flat against the floor/ but by not pressing it - just shouldn't move or arch too much, keep moving one leg out heel against floor (sliding). While other leg is just braced (ie triangle shape). Then other foot. Basically gentle exercise for lower stomach muscles.
https://www.youtube.com/watch?v=_jvUnWbBPXc

Hope it helps.