Wonderful idea and execution. The illustrations help make sense of each area and I liked that you provided a "Lore" and "Guidance" section for each area.
I quite liked the Conductor and the variety of their special abilities, it's a very cool image. I liked that all of the Loot was unique and interesting. I also like the ability to sprinkle in the Musical Puzzles, I think that would be fun to play out at a table - I'm definitely going to use the idea of knocking out a rhythm in some future session.
You really provided a lot of useful content. In some sections there's almost too much. The cover illustration depicting the Conductor is exquisite.