Just wanting to know if this would be able to run a small nas mainly for holding films, tv shows and music and then using use for a plex/jellyfin. As well as a few other docker containers. Would the best os for this use case be unraid and their apps feature or would proxmox be best and then run everything virtualised or something else?
(I would upgrade the amount of RAM)
Yeah, that would work fine. If you need more storage in the future you can always buy a NAS or DAS. If you use Unraid you can boot off a USB stick and then replace that 500gb SSD with a large NVMe and use that for VM storage.