Not much of an answer, but maybe I would recommend not using setuptools, and use any other modern build tool instead, flit might be a good choice, pdm is another one.
Otherwise everything you mentioned rings true to me. Documentation is not as good as it should be, but it is improving by the day, so is Python packaging in general.
Another user posted a somewhat similar post with the idea of documenting their own journey into Python packaging with fresh eyes, you might find something useful in there for you. Here it is:
And the output: