Config. Organization Help

I am completely new to NixOS, but not Linux as a whole. I installed KDE using the graphical ISO and then followed this guide for further configuration. So far the experience has been amazing and I can already see the promise, but I think I need to go slower. I was struggling to update my config and found myself copy and pasting code form AI that I did not understand. I don't want to go down that path. My needs are simple, just standard laptop use, light development maybe for some hobby projects.

In short I am wondering how I should be organizing my configuration. I just want something simple that I can build off of, where it can be clear where programs are and how to configure them and the system as a whole. I generally prefer fewer longer files over many smaller ones, but either can work, I just need something simpler than what I have right now. I can see that the guide I followed is good, but it is too much for me all at once, I'm also not quite sure I understand why home-manager and flakes are needed for a basic single-user system.

The mess I've made so far is in this repo, but I am planning to start completely from scratch. Can you all point me to some templates I could start from or examples I could build off. Or just generally how to go about learning this new paradigm from a practical usage perspective?

Thank You!