I believe these single letter "messages" were useful in quickly determining the day's setup, and maybe wiring diagrams, but I'm not sure about the last part.
Sort of, but that's a massive oversimplification. The bomba machines needed shorts "cribs" of expected plain text to search against, like "heil hitler" as you mentioned, and I think usually they went after the standard start of the day weather report. But the bomba only can reduce the search space, it doesn't produce the answer, and analysts still need to manually break it.
So yes but it was hard so they also took advantage of operator error where ever possible.
