Hi Amol,
"1st" option is not feasible. We have both scenarios where the starting point is either notification or order.
May be I have do the 2nd option. But I have a doubt in this: I'm creating a notification using IW21 and this is triggering an order creation in the background. But after the notification is committed only the number is generated, so is it possible to check this number with the order? so that another notification is not triggered.