I'm using Visual Studio Code for ESO mods, and find the ESOUI forum to be very useful: https://www.esoui.com/forums/
It contains several tutorials, on how to start modding, what IDEs and other tools to use, and heaps more.

This thread
https://www.esoui.com/forums/showthread.php?t=9867
will help you get started, and there's even a fully working example mod to work through here:
https://wiki.esoui.com/Writing_your_first_addon#Addon_file_structure

Baertram wrote: »

btw we call it "addons" not mods! Mods are changes of the total game, and we cannot produce those for ESO.

Before starting your addon PLEASE read if your idea is possible and allowed here:
https://www.esoui.com/forums/showthread.php?t=9865

-> What addons cannot do
And especially:
-> What addons MUST not do

Thank you both for your wonderful replies @Baertram and @vsrs_au
And from a quick look, I think both of my ideas (with a slight perspective shift on one) will work. I will very much do a deep dive into all of those resources both of you linked to before beginning anything.

I think it also depends on the game? eso calls them addons.
Others say mod, like Skyrim.

Nexus mods is just the website name it contains mods, addons, extensions, and other developments (visual enhancements for DirectX, like Reshade etc.).