Well done @JPL - an excellent explanation.
The only tiny thing I would add/change is at the very end.
I have had to try 4-5 or more times with a setup i KNEW was correct. There is a lot of network effort required in initiating a new vault and sometimes the network is busy dealing with other stuff. If your config is correct it WILL work after a few tries.
So don’t give up. Maidsafe are on the bleeding edge of network innovation and by running a vault, you are a valuable part of that effort. Keep trying 