"Must reads" in terms of how to be a writer? If that's your objective, various newsletters are probably your best source of information. The writing market changes so rapidly these days that reference books might already be irrelevant by the time they get to print. Justin Cox, who runs this publication, has a very valuable newsletter. Otherwise, if you have specific questions, feel free to ask. It might be a great source of information for future articles. Also I have a newsletter here: https://walterrhein.substack.com/