The last thing I should mention, gregg, is to have your contractor install a few stick of #3 or #4 rebar into the sides of the slab. This involves getting a hammer drill and drilling some holes in the side of the existing basement slab, and having the rebar extend into the new slab to help lock in the slab and keep it from settling or moving over the next few years.
I don't mention anything about sealing out water here, because you don't mention it as being a problem, but if your water table ever gets above your slab height, you WILL get water up throught the joint in the slab. You might consider some form of draintile for that area to keep yourself dry. (another reason to hire a contractor)