The T5 is pretty straight-forward and there's no need to run encryption on it.
The T7 has some fingerprint security mechanism which is probably best avoided.
The T5 is a USB disk and pretty fast, provided you connect it to a fast USB port which isn't suffering from any contention. I'll let you use the excellent Wikipedia page to determine if you are actuallly using a fast USB port - things are not always obvious.
https://en.wikipedia.org/wiki/USB
Internal SSD is generally more reliable - no cables to go bad, no connectors to wear out etc, but plenty of people run video editing sessions from external drives without trouble. I personally prefer to copy everything to internal SSD and then copy the sessions out to external disk for backup and transfer, but I don't work with video and I'm never in a hurry.
There were some issues with T5 disks and CCC at one point, but these have been overcome with updates to CCC.