Very nice written and well explained.
I would like to add to the backup witness server a note: If you set up a backup witness, choose a different provider. Even better, at a different country. If you host both witnesses (main & backup) on the same provider, they may end up in the same host node (if you are using VPSes), or in the same datacenter. In case of a blackout (power/connectivity/whatever), you are simply paying more to have nothing.
The same goes for the seed node. Do not host it on the same provider. If possible, host it somewhere as far as possible.
And there is always the "risk" of 2 providers using the same datacenter for operations, and they only rent 3-4 racks. You can end up using the same datacenter or even room for your witness/seed operations.
Post resteemed to raise awareness :)
Yes indeed. I didn't go into too much details, I wanted to give a global view of the witness challenges.