Like the others, I suggest you stick to a distro designed for desktop use (Ubuntu, Fedora etc), you’ll have a much easier time.

If you really want to go with something closer to “scratch made” I’d recommend Arch. Its documentation is killer and you can build a system suited to your requirements.

Jellyfin? It’s always supported 4K afaik

And if you’re looking for a way to simplify the setup process: borgmatic

It depends how valuable your data is, what backup strategy you have, and how long you’re prepared to wait to get access to your data when a drive fails.

Personally if/when I migrate my main dataset to SSD, I’ll stick with RAIDZ2/RAID6.

I came to Arch for the customisation, I stayed for the AUR

I’ve seen a few people recommending paperless-ngx