Clarification about raw encrypted backups

Hello. I'm learning this software, and so far I really like it.
After making and restoring local snapshots, I'm trying to make an encrypted copy of a subvolume to an external hard disk, formatted in NTFS. I have the following questions

1) If my backup is encrypted, how can btrbk make an incremental backup? How does it know what changed?
2) Before sending the source to raw, it makes a snapshot of the volume I want to backup. But after the backup is done, the snapshot is not removed, is this the default behavior? Can I safely delete the snapshot afterward?
3) If I want to restore the backup, first I decrypt it, then extract it and after that? Does the btrfs-send&btrfs-receive works with raw .btrfs file?
4) suppose I have a parent backup B1, an incremental backup b1 and a second incremental backup b2 (raw encrypted as described). I don't understand the hint in the ReadMe. How do I restore b2? Should I restore B1 and b1 first and than b2? But how?
5) suppose I want another (encrypted raw) copy to a second external disk, because of redundancy. How does archive differs from just copy paste the raw and metedata files to the second external disk? Or maybe just create a second backup (config identical to the first exept for target path)?

I'm using this configuration: https://pastebin.com/JG3K1SvN
And this is the output it produces when `sudo btrbk -c ~/btrbk/eliminami -v run` : https://pastebin.com/1aGR5rkb

Edit: if this is not clear enough, please tell me. English is not my main language.

Start with the README sections covering raw encrypted backups, snapshots, incremental restores, and archive handling, then reproduce the command using the linked configuration and output. Document the answers to each numbered question, including the restore sequence and whether copying raw and metadata files is supported; done means the README clearly explains these workflows.

Written by the indexing model from the issue text.