The deck gun I can't help with as I can't look at my computer right now.
Most radio messages are purely for immersion. BdU ordering u-boats through the Channel fall into this category. You only have to report to your patrol grid and sink enemy ships - nothing else. Staying out of shallow water is a good idea and you should do it. Sink ships and survive and they will stay happy.
Unless I blow off all my torpedoes quickly, I'm usually at sea betwee thirty and sixty days; sometimes a little longer.