What program do i use to model, texture and animate a mod or addon for gmod becuase i want to start making addons for my server

If you want to make models, you’d need 3ds Max or Blender + SMD/DMX plugins.
If you want to make addons/code, you’ll need a notepad, I recommend Notepad++.
If you want to make textures, you will need a texturing program, Photoshop for example.

To convert to proper texture format ( .vtf ) you will need to either use VTFEdit or a plugin for your photo editing software.

To write .qc files for your model you will need a notepad.

To compile models you will need studiomdl.exe

Can i usgimp since i hate photoshop???

There’s a VTF plugin for GIMP as well.