You can use any computer you want. It is usually enough with something like a raspberry pi (A raspberry pi can be pretty expensive, so you should look for an alternative). Then just connect some external drives (or internal based on the computer).
Do you have an old computer that you can use as a server? If not, you could look for one used. Then get an 8TB disk and maybe a second one for backup if you want to store anything you can’t redownload.
Maybe grab a Lenovo Tiny for cheap somewhere (depending on your location) and add external drives to it. There are really a lot of options.
What are you need and primary usage?