Loading Organizational Plan every week

Hi Experts-

The client is trying to sync up the Organizational plan (Org units, positions and relationships) from external system. We currently have a plan but want to delete it and start syncing up with the external system.

Question I have is-

1. Is there a way to delete the existing plan (all org units, positions & relations) in one step?
2. What happens to deleted object IDs? Are they gone from the system? Can I use the same object ID numbers again?

3. We are planning to do a full load every week. That means we delete what we have and load full again. Is this a good approach? What are the issues with it?

4. Is there a tcode to find out where (which workflows) the org units are being used?

Thanks in advance.