It's true that water of a higher temperature generally dissolves solids better than cold water, but if you're looking to establish and encourage beneficial bacteria, I'd avoid using boiling water - high temps kill the good stuff. Probably not a total kill off, but counterproductive nonetheless.

Remember hearing about how you should boil your drinking water in dire times of contamination? It's done for a reason.

As far as the guano tea goes, I've have good results just using normal temp water and letting it sit for a few days, let the solid matter get good and soaked. Periodically agitate the hell out of it - after a while you'll notice the water maintain more of a constant hue while the gritty, water proof solids stay on the bottom of your container.

Voila, tea time!