Via the GUI your only option is to adjust the throttle options manually:
At least one user appears to have automated pausing of the backup here Backups only during a certain time frame? - #5 by clarityoffline
Absolutely! There are already a few topics about it at Possible to relink an existing backup store (for pre-seeding purposes) and Initial backup to USB then WebDAV. If they can’t help you get it going let us know. 
Technically yes you could as Duplicati doesn’t specifically “hide” anything it’s doing, but the versioning and deduplication process involves chopping files up into smaller (usually 100k) chunks so if a third part tool wanted to access the backups it would need to:
- know the encryption pasphrase
- have access to the archive files
- understand how the individual file blocks are stored and reference (can be gleaned from the archive files but can also be directly looked up in the local .sqlite database)
But as far as I know there are no tools that do that at the moment. However, I’m sure you’d make some people quite happy if you started an Android or iOS app to be able to read Duplicati archives… 