deadlystream.com is a better place for getting mod making help.
There's also a Discord for Deadly Stream and a general KotOR channel with a mod development section.

Tools: It depends on what you want to do. Essential: For years we've used KotOR Tool by Fred Tetra for extracting assets to use as a basis for a mod. Recently there's also a new tool that's still in development; Holocron Toolset by Cortisol. It aims to do the same and some more.

If you want to change textures then you'll need an image editor that can work with Targa files (.tga). I use Photoshop, GIMP is also an option.

There's a bunch more tools to change different assets, for example a dialogue editor, audio convertor, model viewer, KotOR plugins for different 3D modeling tools to edit the models, a simple model viewer to preview your edited texture, etc, etc.

This is a nice intro video by Rece:
https://www.youtube.com/watch?v=85ELbiizTc4

It's best to experiment on your own game, then look into turning things into a mod and then if you like look into making Workshop mods (which has a lot of limitations/pitfalls and is quite frowned upon because of it).

Ah bon, thank you for the help.