questions about a patrol

1: Do you attack every single hostile merchant en route to your assigned zone or rather save your eels for the ones engaged by your patrol grid? Do you let small and medium freighters pass and deal with only the bigger and fatter ones (e.g. 10,000+ GRT). What was the case in real life?
2: Do you attack every single hostile merchant even in the course of a storm when wind speed is 15 m/s and big waves make torpedo failure probability high? Is it worth firing (wasting?) 3-4 eels on a coastal freighter to guarantee the sinking which I'd attack with the deck gun in clear weather? Or is it wiser to wait for the storm to pass and attack only during optimal (or at least more advantageous) circumstances. What did real U-boat commanders do in this case?