Hi Jack,
Based on my understanding, you are using this Custom table for dashboard reports. As others have pointed out that using SAP standard tables are much better than using Custom Table. When we introduce a custom table then we have to ensure the 100% sync between WF and Custom table entries for data consistency.
You could have fulfilled your requirements using few SAP_WAPI* Function modules but If you intend to use the same design , I would suggest not to use the Workitem ID as key field. Instead introduce fields like - Request_ID_No , Item_no , Time stamp (approved on) as key fields along with approval_level_no and status. But then you will have to ensure that the table entries are consistent when workitem is actioned within the workflow process or even with outside influence - workflow admin actions and transactional changes.
Regards
Sandy