In my set up I use Synology. But I would recommend UnRaid. It depends on how much stuff you want to store. A few of the HP Elites have NVME storage expansions if you want to keep the storage in the ProxMox cluster. If you are starting small, I would suggest just starting with an UnRaid set up. Get use to it and learn about storage, virtualization, containers, etc. Then grow into ProxMox.