I actually do like this idea, I just think that without incoming water or outgoing sewage, you really aren't "living" there. Plumbing is the expensive stuff, a electric line is pretty simple. So you could totally "cook" there pub for lack of running water. OTOH you could hook up a hose device from the exterior faucet of your house and be there with running water! Now, just get a composting toilet and baby, you are totally living there!
I assume that you live in a mostly temperate climate. It's good that you carefully planned this according to current ordinances.
Again, I like this idea. I live in a Victorian neighborhood where there are lots and lots of carriage houses over the garages. They are cute when fixed up. I can see a smart single person fixing up the house and renting it, then moving into the carriage house. sit back and pull in the $$$.