I'm currently testing out support center app - Have a few queries.

1. I need to allow engineers to open cases, and add time entries of their work description. But no case closing or deleting capabilities for them. This should be done only by the case manager \ helpdesk agent on recieval of customer confirmation. How can I achieve this - currently if i give view & add capability - the engineer cannot add time entry, if I give edit capability the engineer can ass time entry but can also close the case. Any suggestions?
2. How can I prepare custom report for requests closed by support reps's
3. Where do I find the database schema to prepare custom reports & can i directly access the database schema via external tools?
4. Currently I cannot select sub-accounts while opening cases - if this cannot be done whats the point in having the concept of sub-accounts? (For me sub-accounts are like multiple locations\branches of a customer. Some cases I've 80 to 100 branches\subaccounts for one account\customer). An plans to add this capability? If yes by when?