installer
You mean the “new” installer GUI? I never used it TBH, I always did partitioning (and everything else) via CLI, not sure about that. But NixOS (gnome version) has GParted and all other kinds of partitioning tools on board, so just partition it as you think it’s best and then generate a config via nixos-generate-config
as described in the manual. One tip, when going down that rabbit hole (when you’re committing at least): Start with Nix flakes right away. Checkout all kinds of dotfiles in github of other users (and on github there are a lot of configurations that can be source of inspiration).
Actually it’s been so stable for me for at least a year (not sure when I switched exactly), that this post kind of surprised me, I thought it was > 1.0 already