LW partner is a German abbreviation for Lieferwerk which is nothing else than delivering plant DP.
There is a customizing task for language dependent partner roles in IMG.
Have you read the mentioned OSS notes? If you had then it should have cleared your doubts.
I don't understand why a truck driver has to carry the STO hard copy, do you request the same if you get something from external vendors?
Why is that kind of communication at all needed? Once you completed your STO and saved it then it is immediately available in the worklist of the shipping plant, why an extra paper to tell them that they shall look into their worklist?
What had you tested so far? did you already try to setup mailing between your plants? Have you vendor masters like to the plants? do they have email addresses?