RAID does not work today with any disks you may have: https://www.youtube.com/watch?v=l55GfAwa8RI

.The only sane option is ZFS with zRAID1/2.

An HBA with the SAS cables should run to about £50 used.

Sounds like a good plan to me

I’ve switched to restic for my backups and have been very happy with it. Very fast, encrypted and snapshot history.

RAID gives you greater uptime. That is all. You should also have backups. So how much uptime do you need?