Hi David,
for your 3rd question, SupplierPortalTradingPartner_CreateOrChange_Out is not generated because you have not configured PI. This interface cannot be used with PI independent services. Please check note 1523906 as well.
You will not be able to use this scenario without PI with a standard solution. A non-standard solution would be possible only with considerable modifications to the standard SAP system and code, I cannot imagine a viable solution this way.
regards
Zoltan