That Documentation is not that bad, have you tried playing with it? You won’t find another source to detail all of that, I think, but you can find plenty of examples of the specific extensions.
Try Googling for the names of the extension files (for example, layoutdefs.ext.php) and you will find some pages with examples, these should be enough to get you going. Then come back here with specific questions if you have them.
Thanks, I always appreciate people who are willing to contribute. Remember also another option you have - editing the Docs site with more information. It could be a new Technical Blog post, or some addition to that page I linked above. The site works more or less like a wiki, everybody can edit.
I never saw any, I don’t think there is. Are you using an IDE to develop (like Eclipse or PHP Storm)? This makes it much easier to understand existing objects and code.