The 3b just has USB 2, so even with slow spinning rust, that’s going to be a bottleneck. But it’s probably still plenty fast as a remote storage device for media storage.
Edit: said I didn’t know OP’s use case but in re-reading they did say. Edited accordingly.
I can recommend Debian or Fedora. They are both mature distros that are pretty easy to install and generally work well with minimal fuss and are easy to maintain. I often see Linux Mint recommend, including in this thread. I’ve never used it so I can’t speak to it. But I have every reason to believe it’s a solid choice.
As for transfer process, since you mention using spare disks, NTFS filesystems are supported and you may be able to just copy files off of them. I don’t know if bitlocker is supported.