He'll be fine with fish in the tank as long as it's not overcrowded. I hear alot of people say that it might stress them out but, you've got to figure, wild snappers share the waters with fish. I've kept fish in the tank with my snappers since they were babies and it's also helpful as they'll help clean the tank by eating off of the bottom. For heat, I'd reccomend a submersible heater. I hope you enjoy him I rescued a snapper myself seven years ago when he was about the size of a quarter and now he's huge. Good luck.