John, Aloha from Cleveland Ohio and congratulations on your successful publishing career. I'm more of a book worm than a movie fan, and have been studying the Charlie Chan "Canon" (six novels) since 1997. I can tell you, best place to start is this website. There is quite a bit of info on the site in the "Study". Under "Biggers, Earl D.", click on the following Panama hats to read various prevalent articles: 1)#4-"Creating Charlie Chan"; 2) #6-"Earl Derr Biggers (from Harvard Class...", and #8-"Charlie Chan's Poppa".
There you'll learn what prompted Biggers to write the first novel, how Charlie was never originally a main character, and how the author originally planned on two San Francisco newsmen as hero's in the novel.