You’re sure you’re talking about OnlyOffice, and not OpenOffice. OpenOffice and LibreOffice are related. OnlyOffice is not.
I tried to compare some backup solutions a while back: https://hedgedoc.ptman.name/kket4uo9RLiJRnOhkCzvWw#
Forget about docker. Run caddy or some similar webserver that is a single file next to the assets to serve.
How full is your ZFS? ZFS doesn’t handle disk filling and fragmentation well.
I’m waiting for hetzner object storage (they were hiring some people for this a couple of months ago)
What are the current alternatives?
Depends on your usecase
Prevent password auth and setup sshguard. Wireguard is very nice in that it doesn’t support password auth.
nagios (and check_mk) are plain old tech. Newer ones have been built with lessons learned. zabbix I don’t like because configuration is in a database. prometheus is nice because it’s performant and configuration is in a file (which can be version controlled in git and deployed with e.g. ansible). Data in database, config in plain text files.
I’ve used nagios, check_mk, zabbix and currently using prometheus + grafana. I suggest prometheus + grafana. But you may want to use netdata as the exporter instead of node_exporter. Or both.
rsync + borg, but looking at bupstash
Quite far: