Backing up PVE in itself is not all that useful or even desirable, and should be downright avoided if a member of a cluster- cluster members are cattle not pets.
If you DO want to back up the host (lord knows why) any linux backup method would...
No. that functionality is dependent on your hardware, and might need some intelligence/built tooling by the operator. PVE isnt a storage device.
yes. as a matter or fact, ANY filestore can be used for backup (a SAN would need a local resource to...
that doesnt really mean much. Centos 7 may not be further maintained (EOLed) BY REDHAT but that doesnt mean that downstream users cant backport and maintain their software on their own. its just more work. IBM's decisions to not provide resources...
those two things are not mutually exclusive. xcp-ng uses centos for its baseos and userland apps. see https://xcp-ng.org/blog/2020/12/17/centos-and-xcpng-future/
worth noting that xcp-ng version at that time (2020) was 8.2, and as of 8..3...
so lets put things in perspective- your deluge problem isnt with permissions, its with a firewall.
As for permissions in general, the relevent factors will be of WHO owns your processes; this will be different depending on whether you are using...
Thats an understatement. You have yet to provide ANY argument, data, or reason to validate that assertion. it kinda makes the whole table pointless since you make conclusions without any need for the table.