You're going to need a 3d modeling software (blender, ect), an image processing package (gimp, photoshop), the correct Unity version, a basic text editor like Notepad++, and a lot of patience.
I think the basic workflow is as follows:
1. Model the part in Blender
2. Create texture using Gimp/photoshop and put it on the model
3. Import model to Unity and run the KSPParttools on it
4. Create a config file using the text editor, following config files of similar parts to yours
5. Import into the game
More specifics can be found on the various moding subforums here, and I am no expert in modeling…