a) Not sure what you mean by business object but you can capture the container ID within the Transportation unit within EWM
b) The transportation unit is a Handling Unit within EWM used within Yard Management
c) No, the transportation unit is EWM only and not transferred back to ERP. The OBD is passed from ERP to EWM and back again once the delivery is fully processed in EWM. From what I recall the shipment remains in ERP and is not passed to EWM for processing.
Hope this helps.