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.