Mint works well on my Thinkpads

Debian

It may be possible to create a UI using a monitoring program like Zabbix.

You could create a custom dashboard that displays all the stats that they need to see.

This of course would be for viewing only, not controlling the schedules, retention etc

I’ve never done it so I can’t say for certain.

I typically buy purpose built routers which advertise routing speed benchmarks

It’ll be hard to find one at that price. You may find something with a 2.5G NIC but whether or not it will actually route at line speed is highly unlikely.

Your best bet to keep prices low is to add a 2.5G NIC to an old PC. Even that may not work

Markor on Android and Obsidian on Desktop.

All synced with syncthing

Look at Mikrotik. Very affordable and extremely powerful. Only do this though if you know what you are doing with networking

All my devices use Syncthing via Tailscale to get my data to my server.

From there, my server backs up nightly to rsync.net via BorgBackup.

I then have Zabbix monitoring my backups to make sure a daily is always uploaded.

Brother works incredibly well. Plug and play

Can you send you docker-compose file?