@jessebot @cloudymax infodumps are great, no need to apologize!
For a personal machine, I've found NixOS + KDE Plasma to be...suboptimal. I can go into the details if you'd like, but suffice it to say that I've spent 5 years running NixOS+KDEPlasma on my workstation, and I'm ready for a different set of frustrations. Probably going to try NixOS with GNOME, as Xfce was too much assembly required on top of also figuring out NixOS.
Full disclosure, there's supposed to be a way to run Nix on top of Debian, but I've never messed with it. I too appreciate the allure of Debian, and if not for the absolutely fantastic ease of deployment possible atop a declarative foundation, I wouldn't be on anything else.
For headless stuff, I've found NixOS to be better suited for anything that might change configurations regularly, and Guix to be better suited for things that are pretty much going to stay how they are.