Try 75g. And shubs should be kept at a minimum number of three, no less than that. Even three require a 75g minimum at least to be able to swim freely without additional fish. Nearly all singletails (comets, common goldfish, shubs) grow to 18 inches max. Though it is not often achieved, we should not try to limit the goldfish's potential to grow to its adult size. They also require plenty of space and are best kept in ponds in the long run. Same with slender bodied doubletails such as wakins and watonais.
As with fancy goldfish, it depends which fancy type you get. Orandas, ranchus, lionheads, demekins/black moors and fantails can reach 12 inches. The smallest is a Siamese doll at 6 inches which is very hard to come by unless you are lucky enough to come across one. Fancies in general are more delicate than singletails and fit the tank better. In tropics, they can be raised in ponds.