Misters are pricey, but they are way worth it. One pump can run up to 10 mist heads so you could use one pump for 8 - 10 tanks easily. LOVE my MistKing pump, it is by far the best purchase I made for my tanks.

Grape wood is awful for high humidity tanks. The mold is most likely a gray mold and will make your frogs sick fast. Josh's frogs has a great election of terrarium wood as does NEHERP.

Florescent or incandescent bulbs will kill humidity as well. You can compensate that loss with a large water bowl, a 2 inch layer of Sphagnum moss on the bottom of the tank. Also it helps to remove the plastic and use a damp towel instead. Switch to using a Ceramic Heat emitter at night instead of a feb bulb. It will help keep your humidity up more as the CHE produces no light and is radiant heat. They are amazing heaters.