First step get openBRF on the taleworlds forum to get your items into mount and blade.
Second step get Photoshop cs2 for texturing since it's free because they don't authenticate anymore, or GIMP but I really hate GIMP.
Third step get a modeling software that's free like Wings3D or Blender.
Fourth step is to get Notepad++ for if you want to put your items in-game and test them out. It makes it much easier to put the code in.
Fifth step look up some guides on modeling and texturing and don't give up. Tinker around with the programs and look up every guide possible.
PM me if you like, i'm not a great modeler or texturer but I can help you with any questions you have.