Mixing species can be a tricky thing. Many people don't consider that the animals they want to keep together come from different parts of the world and therefore contain different types of gut bacteria. A creature exposed to a type of bacteria that is harmless to one species might be down right deadly to another. Also mixing species can stress them out as they see each other as competition. If you have enough space, this can be avoided by providing large areas for them to stake out territories. If you're are going to attempt to keep different types of herps together, consider doing it with animals that come in contact with each other in the wild. For instance, you could do a South East United States biotope containing animals such as Green Tree Frogs, Southern Leopard Frogs, Green Anoles, Southern Five-lined Skinks, Pygmy Sunfish, Sailfin Mollies, Madtoms, Mosquito Fish, etc. Remember that space is the key as well so the more the merrier!