I use guix on all of my machines, personal and servers, and have my own guix channel. I'd be happy to answer any questions I can (note that I'm not a maintainer, though I have contributed a few packages).

On top of the official documentation, check out the cookbook.

Also look at David Wilson's aka SystemCrafter's website's guides to guix, as well as his youtube playlist on guix and his dotfiles.

You can also take a look at my dotfiles and guix channel.

Finally if you wanna chat or ask questions, come to the IRC #guix on libera.chat.

Happy hacking!

P.S. About your specific question regarding mixing package versions, look at channel inferiors and guix time-machine.

You can see my post on the situation: https://hexbear.net/post/6283243

TL;DR I don't think you should just switch off of NixOS and give the fash what they want. It is all free software and that means no one has complete and utter ownership of it (nixpkgs has always been a fiercely independent entity who started this whole conversation to begin with).

Otherwise, a lot of the concepts you've learned from Nix (derivations, module system orchestration, etc) can apply to Guix as well and I would argue that Guix is a superior system on a technical level but adoption is still in its infancy and given the smaller community and no infinite S3 compute paid by AWS, updates are slower to roll out.

I've skimmed through the manual and I'm somewhat familiar with lisp and s-expressions and all that because of emacs but there seems to be very little documentation on both the os and the package manager online.

There is a lot of documentation, just that Guix is very much a rapidly developing project (and a rolling release). I recommend cloning the Guix repository (which is a monorepo with everything you need) and reading the source code from there.