Area matters least. What moves a popcorn ceiling project is the state of the drywall under the texture and how high it is — a nine-foot ceiling over a stairwell is a different job from the same area in a bedroom.
Doing several rooms at once is cheaper per room than doing them one at a time, because the containment and the setup are most of the effort. If you are planning to do the whole floor eventually, it is worth doing it in one go.