Homelab

Hey, recently I was thinking of building my own NAS since already "prebuilt" ones are quite expensive. Although the problem is that I don't know much about which components I should pick, my budget is around 500-600 euros for the NAS itself (not including the HDD's) + I'd prefer used parts since newer ones cost much more. And what I intend to use it for is: storing photos, backups, files, movies and probably torrents. One thing to note, I'd prefer one of those small NAS cases (not like the actual PC cases) something like Fractal Design Node 804. Although it doesn't really matter so feel free to suggest anything. Could anyone let me know which parts to get for my first NAS? Thank you.