Hi Tufale,
You are correct on both counts. I especially want to emphasize your second point, only one ProgramID per Listener. More problems come about from reusing ProgramIDs.
Hi Suraj,
Check out the Configuration guide for connecting 12.1 to ECC 6.0. Should cover all that you need to do to set up your IDoc Listener. The differences between 12.1 and 12.2 are trivial and did not require an update to the document.
Regards, Mike