Sorry I did not read every single post here, but wanted to add the ZSE40 actually does report the humidity pretty good, EXCEPT if there is constant motion. So if the sensor is placed such that there wont be motion while someone is in the shower it would then report the humidity pretty well. I tested a ZSE40 and a ZSE11 in the same room during a shower and they both reacted about the same.
If there is constant motion the sensor only reports motion and nothing else, that is the downfall.
I am doing the exact same thing as you, except I chose to use the ZSE11 in the bathroom. Also using a ZEN30 for the light and fan.
This app works pretty good as well instead of trying to make rules, can be found in HPM
