Far bigger than what you think you'll need!

My smallest control box is the one used on my little digitiser (photos can be found at https://www.flickr.com/photos/mc_mtb...57646048305954). IIRC it's a 400x500x150, as I happened to have that size lying around. With that setup, I certainly wouldn't go any smaller, and if I was using separate stepper drivers/controller, I would of wanted something a bit bigger.