Very, I only really use my mouse for playing video games at this point. You don’t really NEED to use Emacs/Vim/etc, but they do help a lot. Ranger (file manager), cmus (music player), qutebrowser (web browser, full featured unlike Lynx, which I do still like, but I use eww in place of it most of the time), etc, etc. Tons of stuff that can make your setup far, far less mouse dependent. Starting with learning the terminal, then using a twm is how I got to the point where I am now where all non-necessary mouse functions are replaced by keyboard keys. Just note that it did take about ten years to get here, though that wasn’t me actively searching for ways to do it, more just naturally making my computer work how I wanted it to without the specific end-goal of zero mouse usage.
I spent about a year in NixOS, and my main desktop still has it, though mostly out of laziness. I did end up switching back to Arch, mostly because if there’s anything you need that isn’t in the Nix repos it’s a pain to install. The other big issue I had was the lack of documentation, so you’ll be figuring a lot of stuff out completely on your own, because Nix works differently enough to everything else that a lot of general Linux resources just don’t apply.
If I had a recommendation for switching to nixos, I’d probably say use the Nix package manager on Arch for a while first, and just slowly switch everything to Arch. It’ll get you more familiar with everything, and then you can make the switch more easily.