Hi Platiesareawesome
Everything I know about goldfish I've learned from JLK. She's a goldfish guru supreme.
The typical rule of thumb for any fancy goldfish is 55 gallons per adult fish. Juveniles you can get by with 30 gallons for the first fish and 10 to 20 for each addition. That said, they grow fast and the bigger the tank you can get, the better. It'll save you money in the long run so you don't have to keep upgrading. Goldfish that are in too-small tanks may become stunted, meaning their outsides stop growing, but their insides don't, which is, of course, very painful.
For example, you could have two fantails in a 100+ gallon. Some people have more, but they have to be religious about water changes because of the amount of waste the goldfish produce. 10 times the volume of the water is recommended for filtration. So a 100 gallon tank would need 1000 GPH filtration.
Basically, bigger is better when it comes to goldies. Bigger tank. Bigger filtration. Equals happy, healthy fish.
It's totally worth all the work and initial investment though when you see those beauties swimming around happily, their gorgeous fins waving.