Mistercharles:
Circuit Design would fall under electrical engineering, this is correct. However, designing the housings would be mechanical. So would be designing thermal or fluid systems which includes all those wonderful pipes and ducts. Personally, I dont know which I recommend. I went mechanical which was interesting, but I kinda wish I went into electrical near my end. It might have just been influenced by an EE professor however, during my senior project.
In either case, MisterCharles, it looks like you want to run your own small business in those fields. Chances are if you are both designing and constructing the product, you'll be in your own or a small business. Or you could just get the degree, be a craftsmen, and use your degree to build your own stuff in your spare time.