If it's a froglet, the small crickets wont work, you will need pinheads or fruit flies. A 5 gallon would have to be VERY temporary, remember, it is a tree frog and they do like their space! If you decide to keep him, plan on getting a bigger tank. Also, if you keep him for a "while" and decide you're done, you shouldn't release it back into the wild. It will get used to having it's food handed to him. If you don't want it as a permanent pet, I would suggest releasing it now.