1. With sync on in Classic all photos in LrM will sync to the cloud and down the folder set in Classic's preferences. To sync to LrM from Classic, would you create Collections and sync them (this would only sync lower res Smart Previews).
2. If the file has synced to Classic then you can delete from LrM and the photo in Classic will not be deleted.
3. What happens when you export to a different location? Is it the same?