first of all you need to install portal plugin in portal system.
then as per sap note for portal configuration create 2 http connector 1 for system other for spml.
you need to create logical port as per note dont remember number you can search.
only difference is you need to paste this in path suffix in logical port.
/GRACAuthMgmtWebServiceOutBinding/Config1?wsdl&style=document
you cannot create shortcut.
SPML connection is used for provisioning
this is used for provisioning and maintained under subsequent connector.
regarding your default role, you dont need that as per your example.
if user select ERP_ROLE 1 , then map portal role to it in rolemapping.
so when user select role1 automatically portal role mapped to it will be selected in request.
Regards,
Prasant