I would not go with procedural textures, would go the "normal" way:

1. Search in the internet for pictures which are fitting to the material you desire (rusty metal)
2. Store them in a folder you find back, while using Maya
3. Structure your Model so that you can use different textures for different Model elements
4.Apply materials to the different elements
5. In the color node of the material you click on the right checkered box, this opens a new menu, where you can choose textures. Click on "File" and the choose the picture file you have downloaded for this purpose
6. All elements of this model with this material shall appear now with the "file-texture" on it

Repeat this for other elements with other materials and texture files.

Hope it helped.

Check out also you tube tutorials - you find tons of it!!!