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
yes
yes
No, fish can't hear.
totally in tanks I've had a fish in a tank and in a bowl and the tank ones lived longer
He named it bubbles. it is a very happy goldfish in a very happy bowl but it died the next day
shouldn't be a problem because they live in both
Well the best thing to do first, when they have outgrown their little tanks, you should get those big tanks with filters. You should get a big one because it would give your goldfish a lot more room to swim.
Most likely a Betta if it's freshwater, because they have an organ called the Labyrinth that allows them to thrive in small tanks. You can also have a goldfish, but it won't be very happy.
If the goldfish is a fancy variety, it can live alone in a 20 gallon tank. Goldfish do not belong in tanks any smaller than this as they grow very large
yes. they can get many diseases from bacteria in tanks and other sick fish.
Probably, but usually the comet goldfish will get all the food and/or the other goldfish will become miserable. This has happened to me before and I do not recommend putting them in the same tanks. Try putting the fancy and comet godlfish seperate!
It is much better for the ifsh if you add a pump or filter in your tank.