To 1)
Better is to use the BackupPlugin, because .config\joplin-desktop is the workingfolder and not a real backup for restoreing.
To 2)
When you edit the not, a version is created and the deleting of resources are depending on your history settings.
https://joplinapp.org/#note-history
https://joplinapp.org/note_history/
To 3)
When you use the same resource id, then the same resource is used.
When you copy the image every time from your Clibboard/PC then every time a new resource is created.
To 4)
Yes, Joplin creates copy's of the Files.
Only if links are used, joplin refers to the original file. This is then also not syncronized.
To 5)
Possible, with the profile switch, but not officle supported.
Under windows you can use symlinks (NTFS symbolic link).
mklink /D C:\Users\<USERNAME>\.config\joplin-desktop d:\joplin\joplin-desktop