Yes, disallow the "Overwrite final results" action on all User Roles
Yes, please read on...
Right click the 'Outcomes' grid > 'Clear this result' or use the Bulk menu.
Enter results for all units and the enrolment withdrawn date
How to result by a client & by Unit
Yes. Have the "Search for existing unit results" option ticked :)
It means no Students have completed the Course.