I recommend that you take a look at LVM. It can help you manage your partitions without much planning beforehand.

In my case all it does is setting DisableAppUpdate to true. So that firefox doesn’t update itself and instead the package manager does it.

You usually scrub you pool about once a month, but there are no hard rules on that. The main problem with scrubbing is, that it puts a heavy load on the pool, slowing it down.

Accessing the data does not need a scrub, it is only a routine maintenance task. A scrub is not like a disk cleanup. With a disk cleanup you remove unneeded files and caches, maybe de-fragment as well. A scrub on the other hand validates that the data you stored on the pool is still the same as before. This is primarily to protect from things like bit rot.

There are many ways a drive can degrade. Sectors can become unreadable, random bits can flip, a write can be interrupted by a power outage, etc. Normal file systems like NTFS or ext4 can only handle this in limited ways. Mostly by deleting the corrupted data.

ZFS on the other hand is built using redundant storage. Storing the data spread over multiple drives in a special way allowing it to recover most corruption and even survive the complete failure of a disk. This comes at the cost of losing some capacity however.

A ZFS Scrub validates all the data in a pool and corrects any errors.