Only Julia can answer that but I'm guessing she does, or at least she does a lot of water changes. Otherwise the water would get too dirty.
Yes you can put it on the back, and as a matter of fact it's the best option for tree frogs, because the heat you get everywhere. Cork backgrounds are cool and you can fix all sort of thing in them
I feed my when they are on the top of the tank. That way they don't swallow anything but the food.
You can use big plants which reach the top of the tank with strong leaves that can hold the weight of the frogs.
Hope it helps