Aiming4 Goldfish Care

I have some questions, can you help me?
1.Regardless of tank size, can you have a black moor, two shubukins,two bubble eyes and 1 comet/common together?
2.what is the rule for fancy goldfish?
3.I went to petsmart the other day and they had like 4 gigantic black moors and some red and white goldfish in a tiny tank, [...]

I have a comet in a tiny tank. I am going to buy a 10gal or 20 gal new tank. I also want a fancy goldfish. Any suggestions? About care? feeding? compatibility? Any thing else I must know?
if you say that comets are not for aquariums than what should i do? freeze her? |:(