I want to create a module / package for NixOS. However, the one I need seems rather compex. Where do I start?

I was looking to manage my server through Cockpit project.

I would like to also be able to use cockpit-machines to manage VMs on my server. However, that module is not present in nixpkgs.

I know how to deploy simple-ish packages, however, JS based projects seem a bit complicated.

https://github.com/cockpit-project/cockpit-machines

Could you suggest a starting point with this project? Any similar modules I can refer to?