The drives were running in RAID mode.
You can do SATA to USB but you need to power the drive separately.
Unless you're doing heavyweight tasks like video editing etc USB class 2 speeds are more than adequate. USB 3 is okay for fast data transfer, but a decent Sata SSD drive is a far better option for game etc.
Everyone who knows anything about computers makes backups.

All my music files, pictures and documents are backed up x3, or the original plus two clones if that makes sense. None are backed up to so called cloud storage.
Hard drives are very cheap compared to replacing 2300 full audio albums for example.