Most of that will be budget based and long term goal oriented. Do you want a 4 bay nas with 10tb drives set up in raid 5 or do you think you’d want a two bay system with 5tb drives set up in mirror raid? Do you want to start cheap and get a second hand thinkcenter off ebay or do you want to buy a brand new NUC and put a 2tb M.2 and 16gb of ram in one slot so you can add the other 16gb later? Some nuc can take up to 64gb of ram and have two 2tb drives in them.
Likely not the solution you’re looking for but a buddy and i link a folder via syncthing and anything added to one side shows up on the other.