If you just want a basic NAS and don't plan on adding any extra features later on, you can't go wrong with TrueNAS, Unraid, or another NAS OS. I'm biased toward TrueNAS, but only because I'm a sucker for a good UI. TrueNAS Scale has official support for the Starr family of software, but I'm not sure about Unraid. If you end up going with another NAS OS, you'll need to do your own due diligence to ensure you can run Starr stuff on it.
If you plan on adding anything extra at any point in the future, use Proxmox with a TrueNAS or Unraid VM. Proxmox itself uses very little system resources and is relatively easy to use. From there you can create add'l VMs to run your *arr apps on.
My motto is: "When in doubt, go with a hypervisor. I use Proxmox on my smaller quote-unquote 'servers' (repurposed desktops) and ESXI on my proper servers. (PowerEdge, Proliant, etc.)"
Hope this helps
DOOOOOOOOOOOOOOM!