Why don't you let restic upload directly to backblaze? I am sure you know this is possible, just wondering on why you made that choice, not trying to be a smartass ;).
I did at first but the latency was a killer; it took about 2~3 hours to make a snapshot. If I did the snapshot locally and then used rclone to back up the restic repo to BB then the whole operation took about 15~20 minutes, and the snapshot itself took less than 5; if the rclone gets interrupted you can just restart it.
