Edit2: OK Per feedback I am going to have a dedicated external NAS and a separate homeserver. The NAS will probably run TrueNAS. The homeserver will use an immutable os like fedora silverblue. I am doing a dedicated NAS because it can be good at doing one thing - serving files and making backups. Then my homeserver can be good at doing whatever I want it to do without accidentally torching my data.
I haven’t found any good information on which distro to use for the NAS I am building. Sure, there are a few out there. But as far as I can tell, none are immutable and that seems to be the new thing for long term durability.
Edit: One requirement is it will run a media server with hardware transcoding. I’m not quite sure if I can containerize jellyfin and still easily hardware transcode without a more expensive processor that supports hyper-v.
Just think of the NAS like a desktop that you ssh into. The only difference is that you install the server version of the distro. If you know how to use a desktop Linux box and configure it via the command like you can do so with a server. It will be the same except over ssh.
Hardware wise, normal desktop parts are good enough to build a NAS. You don’t need to buy anything special that is NAS specific. The only exception might be the case. If you want a lot of storage the case should be able to accommodate that. Some desktop cases don’t have 3.5” drive slots anymore.