This article explains a very important dichotomy that is at the core of much confusion: https://caremad.io/posts/2013/07/setup-vs-requirement/ (by the PyPI maintainer).

Other than that, I don't know of a comprehensive source, in fact have been thinking about writing something myself (if time would allow...). This topic is complex because there is a lot of nuances, and there is no-one-size-fits all solution for numerous Python's use cases.