bathroom on bathroom reno

Hi all!!
hoping for guidence, Wife wants me to redo our bathrooms beginning with the 1st floor which currently is 46" square room with only a toilet. I plan to expand this space for a toilet shower stall and sink. 2nd floor bathroom is directly above and would be renoed after the 1st floor. Plan is to tare out the ceiling on first floor(9ft ceilings) build new ceiling at 8ftand complete 1st floor reno. Then move to 2nd floor tare out floor. now i have exposed floor joists. and about 18"'s of space below them to the ceiling i installed on first floor. this space would give me the room for all new water lines etc. without disturbing newly renoed 1st floor bathroom. Anyone see any great issues with this? Or have a better plan? Any input would be greatly appreciated .

Other than the fact that the PLUMBER might have an easier time installing the piping from the first floor, instead of working from above, it should work. It might just cost a bit more. Unless it is a money situation, I would do both at the same time.