I recently set up something similar to this. I can’t comment on your specific hardware, but I was very frustrated with the limitations of TrueNAS and ended up using Debian and Cockpit with BTRFS for the drives.

I started with two 18TB drives with no RAID, and have since added two 26TB drives with everything’s using RAID1 and ~45TB of usable storage. Converting and adding drives was very simple, but also time consuming of course.