There is no autostart desktop file for Orage Calendar.
xfcalendar.desktop should work after it has been moved to autostart directory.
xfcalendar.desktop shold work after you copy it to the autostart directory?
Yes, but, I think, for end-users it would be better if Orage will be provided in /etc/xdg/autostart/ by default.
The orage project is not maintained anymore and has been archived. Closing bugs.