Sort of. There is no GUI AFAIK, the (easy) way to alter your system configuration is to edit /etc/nixos/configuration.nix directly, make changes there and save it, then update your system with nixos-rebuild switch, or nixos-rebuild switch --upgrade if you also want to upgrade your nixpkgs.
Which leaves the question of discoverability: how can you find out which options exist for /etc/nixos/configuration.nix? That is why I said “sort of”: there is a really long list of options for the stable channel, and one for the unstable channel. Searching through the list matching your channel can be quite helpful.
Yeah the Nix language is worth learning if you’re going to use Nix/NixOS. In fact, your /etc/nixos/configuration.nix file is, probably unsurprisingly, written in Nix.
I can tell you this: Nix may appear a bit strange at first, especially if you’re used to mainly working with mainstream languages in the C family and config languages like TOML and YAML, but it is fit for its purpose like a well-made glove.
BTW, it is possible to use sandboxing for Nix builds. So depending on the properties you’re looking for exactly, there’s no need to choose.
This is an interesting question. It seems that the answer contains a couple of different options.