I went a bit more then a couple hundred, but if you buy some parts used, you can probably get something close to this. It’s super quiet, very low energy use, just works up there on the cabinet in my home office.
Edit: the case is a bit bigger, not exactly sff, but still small enough. The important thing is that it fits 6 big drives and could fit a few more ssds (currently it has 4 + an ssd), and even more important, low power = low electricity bill, low noise = I forget about it.
It runs jelly, hosts my photography hobby, has a few play services I rarely use.
That really depends on the software you use. Some software might have a way to do it, but it may be indirect.
E.g. digikam is a photo library management software. It can move albums between “libraries”, and is designed that some of those libraries can be offline occasionally (more in the sense of SD cards, but also e.g. USB storage). So how you could do it is you map one, mountable, library to one disk, another to your “network storage” (however you attach your home server). That includes the metadata (depending on where and how you store it). And the digikam database itself is just a file as well (sqlite database), so you can also back that up at the same time. I’m not sure how to automate this process. Even a manual “cheat” - moving the files to network drive, then symlinking it back, per month or something, might work. It’s a bit of a manual process, but digikam is designed to be storage-based. And a lot of other software is, as well.
But again, I don’t know if you’re using digiikam or something else, and how you set it up. So, what software do you have? How do your users sync their photos and albums? That might help planning.