For juveniles the 12x12x18 would be appropriate, minimum 18x18x18 for adults.
True. Treefrogs are sensitive to D3 supplements and UVB is a safer and can be regulated by the frog... then use something like Repashy calcium plus LoD for dusting. Exo Terra have an app for helping with getting the right UVB bulb called UVB buddy or you could contact Arcadia reptile lighting who are experts on this subject. The joshs frogs care sheet is pretty much what you get everywhere on there care but there's also this one
http://www.reptilesmagazine.com/Care...og-Care-Sheet/