Awww, he is adorable. I have two Grey Tree Frogs. I know one is definitely male as one croaks a lot - also I've been reading that males have yellow on their back legs. It gets brighter when around another male is around as sort of a warning type thing. If by Small Exo-Terra you mean the 12"x12"x12" - that should be fine to house just one Grey Tree Frog. I have the 18"x18"x18", I believe and have my two in that with PLENTY of room. I see them perched near each other all the time, though.