not better in groups
Yes.
sometimes if there in the mood
goldfish live in groups called schools they don't go to school there group is called a school
Goldfish spawn in groups in springtime when the water temperature approaches 70F. They do not have live babies.
Normally goldfish are peaceful and calm.But incase your goldfish is doing so then its better to separate the new goldfish.
No, they can't. Trust me, the terrapin would rip it to shred's.
cause it can breath better
That is a matter of personal preference. Read the ingredients on the label and make your decision based on the higher the amount of protein the better the food is for goldfish.
cold is better cuz when your in the ocean is the water hot or cold cold
Yes, the bigger tank the better. They actually HATE goldfish bowls. (they're not nearly big enough). Goldfish usually need a 20 to 30 gallon tank
feeder goldfish you can also use minnows but feeder goldfish are better because they are bigger they are about 30 cents each
Goldfish food is commercially available at most pet shops. But I believe you would be hard pressed to find a better food for goldfish than Earthworms.