TW,
Thanks for sharing the process.
I believe you are on the right track. Unfortunately not all external systems have a good in-built pack optimization algorithm, so in your case it looks like SAP is the leading one for pack proposal. If they are able to send you the changes per packID - quantity and packaging material, then it is very good. Do you use automatic adjustment of delivery quantity to the picked quantity at shipment loading end (if you use transportation of course) or at some other event? It might make the things a bit easier for the warehouse employees.