(Re-)Installing NixOS

I’ve been using NixOS for quite a while, but didn’t really commit to it at first. This resulted in Windows taking up most of my disk space and I tried to be clever with partitioning too .. which bit me a lot. And that’s the main reason for reinstalling NixOS this weekend: I need disk space! My root partition has a size of 10G, because that ought to be enough, when I’m saving large stuff like games elsewhere, right?