I got it! I am able see successful Jack startup with the bluealsa (bluetooth) destination, after rebooting a few times and verifying Jack service status via SSH. Expect a final reply to this post by the end of the weekend with a link to a new ‘guide’ post with every step.
It’s still not optimal. I could not replicate the success of (in jack.service) using After=sound.target bluetooth.target when starting from a fresh image (to delay Jack start). I ended up adding an ExecStartPre=/bin sleep 15 to jack.service to get consistent auto-pairing and jack start in time for login. I expect there are better ways to make sure Jack gives bluetooth enough time to complete a connection.