Poetry2nix is your best bet imo, and read through this doc carefully https://github.com/nix-community/poetry2nix/blob/master/docs/edgecases.md. The option with pypkgs-build-requirements was how i managed to build a mid-sized django project successfully. For IDE i have a devshell set up that pulls in a configured nvim with a python LSP, formatter, debugger,... Works fine for small scripts but i would just use Pycharm in your devshell if you're on a graphical machine and then also use nix to pull in python with packages. If you use venv i think you will need to also use https://github.com/Mic92/nix-ld

Oh my god this is amazing, will definitely give it a try!

This seems like it directly uses nftables rules, but ive seen a couple of aspiring Nix router repos that already offer nix module configuration like https://github.com/chayleaf/nixos-router that dont require you to be a networking expert, however it seems to be a long way off from a featureful router system. If you are after a declaratively configured router i would just go with VyOS.