That's not true. You get support for the part of the guix system that is free software from guix, and support for what comes from nonguix, from nonguix. So if you have issues with the proprietary driver, you talk about it on #nonguix, but if you have troubles with guix, you talk about it on official channels like #guix.
The main guix "channel" (that's what it's called) contains more than 17.000 packages. Some software is hard to package, but I can't think of anything that's missing from the repository. You can have a look at the list of packages at https://guix.gnu.org/en/packages/ (note that firefox for instance is called icecat and based on the ESR version).
There are no other official channels, but a bunch of people have their own channels with additional packages. The most popular is probably nonguix (https://gitlab.com/nonguix/nonguix) which provides some popular nonfree packages.
Creating a recipe is generally easy (it's just a bunch of metadata) and even easier if it's supported by one of the importers (python, perl, emacs, ...). You can use guix on any other Linux system if you're not ready to install the complete system. The only difference is that your system is not managed by guix, and you can't run "guix system reconfigure", but the experience is otherwise the same. Make sure to follow the additional steps from the manual.
I usually carry a few stickers on me just in case, so people can remember OSM and look it up later (after I explain what I'm doing and say it's a fun community project).
https://framagit.org/tyreunom/guix-android