Smashing Magazine’s take on “Extending WordPress With Custom Content Types” is one of the best I’ve seen around. It is very complete – skipping only, from what I can tell, the REST API functionality of the custom post types. It’s easy to read and follow. It has both screenshots and code snippets. And it is based on a real example.
This article alone can answer a gadzillion of those “Can this be done in WordPress?” questions.