What is an appropriate humidity for separating curds and whey? Does anyone have guidelines for an appropriate humidity for separating curds and whey to make cheese (I'm doing it from kefir)? Specific temperatures are available, but sources I've seen just throw in "and humidity can affect the outcome too" without giving anything concrete.

I'm not sure if wetter is better, dryer is better, or, more likely, if there is a specific range.
86 degrees Fahrenheit (with citric acid added before the heating process, if you want mozzarella/ricotta curds) or a culture added after this point (if using a culture give it 1 hour to start reacting and forming acids) rennet will need to be added in both cases. The temperature should be held at 72-77 degrees during the separation process. Humidity will not really have any effect on your cheese or kefir during the separation process.