I have done a little research, mostly before I got Beau, and I know that a fish will only get as big as it's environment allows. Granted I have not seen the fish yet, but as the four of them are in a peanut jar and have space to move around, I don't believe that they are huge. At most I expect them to be 2" or so.
This is false. Fish do not grow to their environment. What happens in these small bowls is that ammonia and nitrate build up to such levels that the fish has to deal to put all of its energy into dealing with these problems instead of growing. Basically you're stressing the fish into a stunted life. The organs do continue to grow inside the fish. The fins will look funny, and usually the eyes are abnormally large. This eventually causes the fish a premature death.
If the water in a small tank is kept clean, the fish will continue to grow.
I was also doing some reading up on goldfish tonight, and everything I'm reading says to not go above 60 degrees, as they are a cool-water fish.
Again, another falsehood about goldfish. They are extremely temperature tolerant. Mine get up to 80F in the summer just fine. The thing about goldfish and temp is that as the water gets warmer, they need to be fed more often to maintain a good weight (ie not becoming underweight) and this causes them to produce more waste. In warmer water they also need more oxygen. So while they need more care in warmer water, they can certainly do just fine in it.
For food, again this is going to depend on whether or not they are fancy goldfish. For common goldfish, any high-quality pellet food will do. For fancies, even with high quality pellet you can run into problems with bloat (and they actually get worse with lower temperature). Right now I just recommend getting a good quality pellet like Hikari Saki or New Life Spectrum. Fruits are okay for goldfish but only in small amounts. Leafy veggies are the best for them. Things like kale, spinach, and red lettuce are the best. Mine also love zucchini.