Emacs lisp is something you can figure out a bit at a time: mostly you're writing 'snippets', rather than organizing some huge codebase where you have to know all the ins and outs.
I second this. At my first Real Job after university, I was challenged by a teammate to learn to use Emacs. He laughed at how primitive my (non-Vim!) vi editor was. In hindsight, it was absolutely true. I bought the O'Reilly book for Emacs and spent many weekends teaching myself the basics.
You are right: Bit by bit you write tiny macros that do things you need or want. After 1/2/5/10/30 years, your personal macros compound to create real efficiency. I don't use Emacs today, but I do appreciate that the ecosystem is enormous and well-developed.
I agree that elisp, itself, is quite easy to learn. I wish I could say the same about the emacs API. M-x apropos is somewhat useful, but quite a lot of my editor customizations come down to either 1) reading the source of the functionality that I'm trying to customize and reading what variables it accesses or 2) random Googling to see what others have customized.
That said, to emacs' credit, it makes (1) extraordinarily easy. C-h k to see which function is being called by a given key-combination and C-h f to get to the source of that function makes it very easy to look at the internals of the editor and figure what I should setq in order to make the editor behave in the way I want.
For Common Lisp: Practical Common Lisp is a good introductory text. ANSI Common Lisp is older, but still relevant (the standard is from 1994, it hasn't changed, though the community and tooling has the language is stable). On Lisp and Let over Lambda are good follow-on texts if you want to learn about macros, in particular. Common Lisp Recipes is another good one for after PCL.
For Emacs Lisp: I just looked at the info pages for emacs. There are some books, never touched them so can't comment. But if you know CL, Emacs Lisp is not a stretch to learn as it's about 90% the same (especially since they made some changes in the past decade or so to better support lexical scope by default).
For Scheme: Check out The Little Schemer and the rest of that book series. Unique presentation style, but very approachable if you get past it (some people don't, I liked them).
Back in the day I started out with the "Emacs Lisp Intro" also known as "An Introduction to Programming in Emacs Lisp" that comes with Emacs. I remember printing it out and devouring it before going to sleep.
It looks like it's been kept up to date and you could do worse than starting there, especially in an Emacs context.
Here is the online version in case you don't know how to navigate info manuals yet:
