You are correct on both points. The myth that Churchill sacrificed Coventry to keep the Ultra decryption secret was (I think) first brought up in the book Intrepid. The British historian and politician Nigel West (real name Rupert Allason) has debunked the story in one of his books. (I think it was Counterfeit Spies, but like you I am not quite sure.)
A very interesting discussion and for sure Beamis photo documentation will be well worth watching. From a marine archeological point of view it will be very interesting to get more information on the sinking of the
Lusitania. However, whether she was carrying munitions or not is a moot point.
She would have been torpedoed anyway - for the simple reason that the German U-boat commander, Kapitanleutnant Walter Shwieger on the U-20, did not know it was the Lusitania he had hit until she started to sink. (The U-boat war 1914 - 1918, Edwyn A. Gray).