The problem is that the anemometer impeller and the output fan both have too much inertia. The anemometer impeller is incredibly sensitive, but once it starts spinning it can take several seconds to stop, even without any breath. The fan is the same way, once you turn it off, it takes several seconds to spin down.
So I am contemplating redoing Breath-over-IP using a servo motor and servo controller. This should allow me to speed up and slow down the fan motor very quickly. On the breath sensor side, I could use a pressure sensor chip.
Finally, I'd like to solve my networking challenges using a plug based Linux PC with a USB-attached Arduino. That way I can do very complex networking in Python on the plug computer, and let the Arduino handle analog/digital I/O, which it does well.
So that's my plan...