In space, no one can hear you flush. :)

I respectfully disagree with Daio's prioritization.

Make the corridors first, so we can link all of the sections together as they're released.

How about elevators, ventilation shafts, and Jeffries tubes (or whatever they're called in non-Trek parlance)? You know: the unpleasant, claustrophobic bowels of the ship, where you least want to encounter a hostile lifeform.