Thanks,
I've manged to get my quest started by adding a new quest node to the stacked branch node then used the GetStageDone condition which is exactly what I wanted.
Manged to get the courier to deliver my letter using:
Alias_MyLetter.GetRef().Enable()
(CourierQuest as WICourierScript).AddItemToContainer(Alias_MyLetter.GetRef())
I get the 'Item(s) added' notification I don't suppose you know if there is a way to make it say 'My Letter's name added'