You can pick any hard drive, preferably a NAS/Server Oriented one.
They do have to match if you’re doing a multi drive RAID/ZFS though.
It’s kind of complicated, if you can afford the lifetime price, HexOS has some amazing things going for it as a fork of TrueNAS, but TrueNAS is FOSS and has probably everything you need, if you’re planning on doing Jellyfin, you might wanna stick with TrueNAS Scale.
I presume you acknowledge the risk imposed going through the Custom NAS Route yes?