1. The permissions you need to grant in order to save your settings only allow the app to read and write its own configuration data using your Drive storage quota - it does not have any kind of access to your Drive documents. I will update the Privacy Policy to make this clearer.
2. You can either de-select calendars in Google Calendar and reload the page or hide calendars using the buttons at the bottom of the page - in this case, the calendar would still be synced but you wouldn't see the updates.