My fave theatre- related books are, off the top of my head:
Not Since Carrie: 40 Years of Broadway Musical Flops
Everything Was Possible: The Birth of the Musical Follies
Ghost Light
Making It Big: The Diary of a Broadway Musical
A Chorus Line and the Musicals of Michael Bennett
Second Act Trouble: Behind the Scenes at Broadway's Biggest Bombs
Steven Suskin's Broadway Yearbooks (I think there are 4)
Scott Miller's directing specific musicals books (Rebels With Applause, Deconstructing Harold Hill, From Assassins to West Side Story)
Let the Sun Shine In, by Scott Miller also
The Season!!!
Broadway: The American Musical
Ethan Mordden's series
Hot Seat
Making It On Broadway
The Theatermania Guide to Musical Theater Recordings
[title of show] on Broadway. it's time. believe.