There’s different kinds of backups. For this you don’t need off-site storage.
For this I set up zfs auto snapshotting which means when I delete stuff it isn’t really deleted because a snapshot is still pointing at it until it rolls off the time window.
Both zfs and btrfs can do this but you do need to change the filesystem to use these which can be a lot of work.
Probably just go with SSD storage because 2T is fairly low for hard drives these days. Still a pretty good idea to do a mirror.
Pretty much any CPU that isn’t a raspberry pi will comfortably max out a gigabit Ethernet connection.