The last few months I\'ve been using Emacs extensively as my main development environment and I\'ve now come to a point at which I\'d like to learn it\'s own Emacs Lisp to w
Start with Emacs Lisp (given that you seem to have already started customizing your emacs) - it seems to be more immediately useful for you.
Do keep in mind that there is quite a bit of difference between Emacs Lisp (there is a lot of buffer management stuff, especially in the code you're likely to see in the wild) and Common Lisp (more similar to a general purpose programming language), so which ever route you take, expect some amount of "wastage"
I recommend that you start with EmacsLisp, as it will be more immediately useful as already stated.
And as soon as you get a good grasp on the peculiarities of the language, you could start usingeieio
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To quote the emacswiki, it is An implementation of the CommonLisp object orientation standard (CLOS) in EmacsLisp
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Best of both worlds !