If you want to start heavy customization you can start by looking at configurations in literate programming style, you will learn a lot of documented customs.

Here is an exemple : https://github.com/vdemeester/emacs-config

Also about the book someone on #emacs said it's mostly tips for beginners and about 14 more for intermediate users. I'll suggest you to read the website first and see if you like the author style/pov