For humidity, keep it as a rule of thumb that if their is condensation on the inside of the glass, then the humidity is high enough. Idon't even own a humidity gauge, and I have 7 frog tanks going. I have never had a problem with humidity.
Temps, remember where they come from, and sometimes their habitat can drop down below 65 easy at night. Better to keep them on the safer side though, never above 80, never below 65? (correct me if I'm wrong). As for temperature control, you can run a thermostat on some incandescent lights, use a fish heater in a water fixture (drfostersmith.com has really good ones, with the heating element separate from the control unit. So makes it incredibly easy to adjust temperature outside of the tank, and they are only like 10 to 15 dollars. I am unsure of the exact website, but it is dr. foster and smith. You can find them in the classifieds at kingsnake.com under the fish and aquaria section.) Also, a running water system can act as a heat sink, which will lower temperatures if they are too warm. Ice over the lid is a good way to control temps if they get to high. Best way is to keep them in a room with its own a/c and heating though.
Feed froglets small amounts everyday. If they haven't totally finished their flies from the day before, feed them fewer at each sitting. If they have finished them all, feed them larger quantities each sitting.
Good luck with the leucs, I have never kept these yet. They are pretty neat frogs though.
Ed Parker