Good mission, nice bit of detective story. I actually had the pleasure of hearing Beethoven's 7th symphony in concert recently.
Out of curiosity, spoiler:was Nathan Hunter one of the prisoners listed in Cragscleft from Dark Project?
One large gripe, however: spoiler:the loot requirement on expert is too high. After playing Thief for more than a decade, I have no desire to be forced to find 98% of the loot in a mission before I can finish. It's just not interesting to me. In your second mission, I recommend lowering that percentage to around 80%, and if anyone wants to go hunt all the loot, that's fine.