...Not sure how I feel about dragging in non-author-based real people as characters. Specifically, do you actually know enough about the man to be sure he'd go for this? For that matter, do you know enough about him to be sure he'd be any good at it?
Beyond that, though, you forgot to mention his status as a beloved rock star in Germany.
Beyond that, though, you forgot to mention his status as a beloved rock star in Germany.