I want to build a local storage server.

Basically like a storage pod 4.5, but not 10,000$. I would like it to be upgradeable, so it could start at maybe a few 4TB hdds, and then i could buy more as desired.

So my question - how do i get started? What do i need to buy? Which distro would work best for this? I want to manage this remotely/from my laptop (but not over the internet. Just over the local network).

Ideally, the server itself won't have internet access at all, but will get everything from other computers on the network. And if possible, i would love to use it like local storage on my pc or laptop. So if i download something, it just saves to the server storage.

Thanks for any help.