In the many things I watched, one of the big tech reviewers (GN I think they're called) said it seems like the Synology units have power issues after not very long in service. They had multiple units (of different models / owners) fail all within like 6 months of service. Otherwise, they looked nice with the whole hot-swap / rebuild method. The data's not really being accessed much at all, so it'd be more of an archive. Give or take me adding ISOs or Finally getting on that media archive project. It sounds like the recommendation here is to get the 4-bay unit though, even if I'm not yet using that many drives.
As for RAID itself, I thought it was best to have these things in pairs +1 for parity? I've read that RAID 5/6 are designs to be avoided and I think I remember RAID 10 (1+0?) being the best for redundancy / recoverability. I stumbled into the software RAID world around the time I came across the (don't laugh) LTT videos on the horror stories Linus has heard about standard raid (parity drive pushes corrupted data to good drive, etc). The RAID F1 vs SHR was interesting to read through and the advantage (when using the boxes) seems there for sure.