dream on mcss,
Man, never stop dreaming! The future is built from dreams but, some dreams don't build squat!!! That said, talk to your building inspection dept.. You'll know for sure what the minimum required material sizes you'll need to use ( the size of your dirt cheap cement blocks might not be legal for your project). I think you'll need more then 10 feet to install your stairwell (I suppose you can put your sump pump under the stairs). Oh, and if you decide to build this without a permit, you could face a fine (that will be alot more then the cost of the permit) and could be made to dismantle your project. Also, it'll be awfully hard to hide the minimum 16ft. x 16ft. hole in the ground (you'll need room around the outside of the block walls to do your water proofing), especially if you have enemies (for lack of a better word). You'll also need to know property line set back and the distance from existing buildings. Height restrictions of the shed.
I started hounding my inspectors about a year before moving even a shovel full of dirt. They could see that I wanted my shop built right the first time around, and they were glad to help me in the planning. My inspection were uneventful too.
These are just a few things to think about and, keep on dreaming!
Doug