Any text editor will do, as the file is pure text. But those for programmers are better, like notepad++ or sublime, both very good editors.
Not necessary, the game recognizes folders as mods too. You can zip it again and rename the zip to .smod, but we just do that for easier sharing and to avoid users damaging the mod by accident while messing with the files inside.
There is not much tutorials (if any). What we have are simple mod “models”, that we can look to see how it works, basically what you are already doing, but doing simpler things. Startermod_basic updated with weapons, armor, lights, and particles