KDE Sytem monitor has that function, too. You just have to add it to the history page (Sensors/GPU/Usage)

You can access ZFS snapshots from the hidden .zfs folder at the root dir of your volume. From there you can restore individual files.

There is also a command line tool (httm) that lists all snapshotted versions of a files and allows you to restore them.

If the snapshot you want to restore from is on a remote machine, you can either send it over or scp/rsync the files from the .zfs directory.

Yes, it does. You can also use the tool to check if a file is cached (just run it without any arguments for that).

If you use a VPS as a backup target, you can also format it with ZFS and use replication. Sending snapshots is faster than using file-level backup tool, especially with a lot of small files.