Saving the concrete flooring for last is the correct way of doing it, if you plan on a lot of weight being on it. If the floor drops because of the weight, your walls will not crack. It's called a "floating slab" and the only problem with them are ants coming into the building, being there will be a crack between the floor and walls. Not sure why you would use rebar when a 6" X 6" wire mesh would be fine. Sometimes I would use rebar at corners or any other weak areas, as a thin spot, but not everywhere. Poured a driveway once and did use rebar because it was used for a heavy tile truck, that would be loaded at times. Gross weight was, 12,000 lbs.
