You spent a lot of time writing this extremely detailed post, and I commend you for that.
But I’m going to give a short reply, and I hope you don’t take offense to that.
Don’t combine everything you want into one box. It’s going to cost way more than it needs to.
Separate 2-3 machines out for dedicated uses:
- NAS
Where all of your storage is located. The hardware requirements for a simple NAS are super low, like the NAS Killer 4.0. - Plex (QuickSync)
HP 290 or similar dedicated transcoding box, like the OTiS. - BlueIris (QuickSync)
Again, HP 290 or OTiS.
Even the lowest end recommended QS CPUs can handle 20+ transcodes or 6 1080p cameras.