Hello! I can answer a few of your questions. First of I wouldn't house different species together, but a frog and a newt may work but you would have to ask the other members about that. I use a 15 gallon tank for my pacific chorus frog as for the newt they need 15 gallons... I would use a 30 gallon semi-aquatic setup for those two animals if you did house them together. As for the 3rd question I am not sure as I do not keep rough skin newts. I hope this helps!