I just got a Chubby frog at a pet expo. This is my first frog but not my first amphibian, I have some questions.

I was going to put it in my 20 long but would he do better in something smaller? (15, 10 5 gallon?) He's only about an 1 1/2 long.

Does he need heat? The guy said room temperature is fine. I live in Canada and my house goes does to 60 degrees at night.

Are earthworms an okay staple?

Thanks in advance.