(I'm also learning English, so I know that having your mistakes pointed out helps - that's what the [] are for in the quote)
Yeah, been there, done that. :) Docstrings and easy access to source code (find-function, find-library) are a great strength of Emacs - not only the documentation is of great quality, but it's mostly up-to-date. But going through packages' sources is not always pleasant: some authors are not very good with English (like me, for example), others have a dislike for writing comments, yet others are biased against cl-lib or too much in favour of eieio and so on. It's still a great learning experience, but it takes more time than it could take if the content was presented more systematically and in a more readable manner. Like in a book. Or a series of articles, or something. Note: I am thinking about writing something like this myself, but I don't feel confident enough just yet.
> someone advised me to stick to stock Emacs
I think it's stupid advice - bad for both programmers and non-programmers. If you're a programmer, using Emacs is (should be) about endless customization, tweaking and - you guessed it - programming your editor to do your work for you. In this case learning to use C-f instead of right arrow is so stupid it hurts - you should learn about define-key, make-sparse-keymap, global-set-key, describe-keymap (and generally describe-...) and of course apropos instead. I guarantee it will take you less time than making C-f a habit! That's the way I learned Emacs: I started learning with Emacs Lisp Manual, not a tutorial or Emacs Manual and it got me up to speed in no time at all. Instead of learning what keys to press to do something it's better - again, for programmers - to just learn the name of a function which does what you want. It's true that I don't use many standard keybindings and I remapped most of them, but this is ok, because this is my editor and nobody else is going to use it anyway. And when I started fiddling with packages I already knew how to hack them into shape and dig through their code, which is infinitely better than just knowing where to find them and praying they have any docs at all :)
And for non-programmers, sticking with vanilla Emacs makes it unnecessarily painful experience, with 2/3 of useful features disabled by default and without access to the functionality available via packages, which I'd call really essential. For non-programmers vanilla Emacs is not that much better than Notepad++ or Gedit (if at all, considering weird key bindings!) and it's pointless to stick to it just to "learn about Emacs philosophy" - non-programmers won't benefit from "the Emacs way" (which is: being an infinitely programmable editor!) at all. It's much better for them to grab some Emacs starter kit, like Prelude or any other starter kit out there and then use customize-... interface to tweak what they need.