I bought a 5,000 square foot victorian mansion that was built in 1896. I noticed some water damage on the ceiling of the first floor. I believe it is coming from the bathroom on the second floor. The toilet had a leak and you can tell it is getting bad just by looking at it. The floor does not seem stable when you use the room in that area also. I know it is probably wood rot but will there be mold when I take that apart? If so how can I safely remove it?
Once I get that floor up I am sort of confused on how to go about replacing the floor. If there is no floor there I will fall through

Any assistance would be much appreciated!