1. Automation: you made everything correct. It is intended to work that way - if it failed - it is a bug!
2. Would be useful if after upload the file/folder appear on screen: I agree! I opened an enhancement ticket on GH. I will fix that part in next release.
3. I didn't get the Inbox folder meaning. I suppose I can send emails with attachments and the attachments would be stored there?: Correct! Even more, you can import documents from you local storage and all imports will appear in Inbox.
4. Should the "Documents" folder appear in a tree-style on the left pane? Maybe collapsed from start? Well, in theory yes. In practice it will take some time until UI will look like typical desktop file manager.