I’ve been daily driving NixOS for about a year now, switched from over two decades of running Debian. I’ll try to answer your questions from my perspective:

How much can I grok in a week?

If you have some experience with functional programming or declarative configs (think Ansible), then it’s a lot easier. You can definitely learn enough in a week to get started. One year in, my Nix knowledge is very light still, and I get by fine. On the other hand, there’s a lot of Nix I simply don’t use. I don’t write reusable Nix modules, and my NixOS configuration isn’t split into small, well manageable files. It’s a single 3k lines long, 130k sized flake.nix. Mind you, it’s not complete chaos: it is generated from an Org Roam document (literate programming style; my Org Roam files are 1.2mb in size, clocking in at a bit below 10k lines).

With that said, it took me about a month of playing and experimenting with NixOS in a VM casually, a couple of hours a week, to get comfortable and commit to switching. It’s a lot easier once you switched, though.

How quick is it to make a derivation?

For most things, a couple of minutes tops. I found it easier to create derivations than creating Debian packages, and I was a Debian Developer for two decades, had a lot more and lot deeper understanding of Debian packaging practices. It’s not trivial, but it’s also not hard. The first derivation is maybe a bit intimidating, but the 10th is just routine.

Regarding make install & co, you can continue doing that. I use project-specific custom flakes and direnv to easily set up a development environment. That makes development very easy. For installing stuff… I’d still recommend derivations. A simple ./configure && make && make install is usually very easy to write a derivation for. And nixpkgs is huge, chances are, someone already wrote one.

How quick is it to install something new and random?

With a bit of self control and liberal use of direnv & flakes, near instant.

How long do you research a new package for?

https://search.nixos.org/packages, you can search for a package, and you can explore its derivation. The same page also provides search for NixOS options, so you can explore available NixOS modules to help you configure a package.

Can you set up dev environments quickly or do you need to write a ton of configs?

Very easy, with a tiny amount of practice. Liberal use of flakes & direnv, and you’re good to go. I can’t comment much on Python, because I don’t do much Python nowadays, but JavaScript, Go, Rust, C, C++ have been very easy to build dev environments for.

What maintenance ouchies do you run into? How long to rectify?

None so far. If it builds, it usually works. I do need to read release notes for packages I upgrades, but that’s also reasonably easy, because I can simply “diff” the package version between my running system, and the configuration I just built: I can see which packages were upgraded, and can look up their release notes if need be. In short, about the same effort as upgrading Debian was (where I also rarely ran into upgrade/maintenance gotchas).

Do I need to finagle on my own to have /boot encrypted?

If you use the NixOS installer, then yeah, you do have to fiddle with that a bit more than one would like. If you install via other means (eg, build your own flake and use something like nixos-anywhere to install it), then it’s pretty easy and well supported and documented.

Feel free to ask further question, I’m happy to elaborate on my experience so far.

Meson and CMake are the two major players I’ve seen along autotools. Are they better? In some respects, yes (especially Meson, imo), in others… not really. For a pet project that only targets two platforms, I’d just stick to handwritten worst-practices Makefile. You will likely have less trouble with that than any of the others, simply because you know it already.