unraid 100%

I use open media vault at work. It'll run on a potato.

Some variation of Linux + BTRFS filesystem + Docker is what I use. Lots of good options for free.

Debian with ZFS and Docker would be my recommendation.

I use Ubuntu + ZFS.

ZFS is cool because it has built in SMB and NFS file sharing, on top of RAID and data integrity features.

Unraid- if your drives are different sizes. Truenas - if you have lots of ram and like ZFS. CasaOs - If you like pretty things. Proxmox + Open Media Vault - If you want to run vms.

I’ve only ever used Windows. Isn’t finding drivers on those other OSes a headache?

I like synology for simplicity. And because I believe it‘s hard to get proper alternatives for synology drive and photos

Certainly some variation of linux, but there are many of those. For drive pooling, your options are btrfs or zfs. Of those, zfs is the most mature and capable - the only drawback is that once you make a pool you can't easily change the number of drives in it. A small limitation.

Drive pooling as ZFS does it is a replacement for RAID. You generally don't need RAID these days, except for fault-tolerant boot drives in high-availability servers.

Ignore the ZFS "1GB per TB" thing. It's old advice. Use, ZFS does like lots-o-ram because of the way it uses caching. But it doesn't need that much. Your 16GB plan is plenty. You could probably do it in 8GB.

TrueNAS Scale if you want something relatively easy to use with prebuilt applications (see TrueCharts)