Yes, The water will get cloudy and your fish will be unhealthy if you overfeed them. Feed the fish how much it can eat in five minutes once a day. you can feed them twice a day as long as you be sure not to go over the five minutes per feeding. Be sure to remove any uneaten food from the tank the best you can.
Fantail goldfish are a hardy breed, strong swimmers and they compete well for food with the ryukin, shubunkin, comet or common goldfish; making these goldfish breeds good tank mates for your fantail goldfish.
they will die
yes
Female Fantail goldfish can not get pregnant they lay/scatter eggs when they are chased by males . So you have nothing to worry about.
Goldfish are peacefull fish and do not normally fight with one another.
it has a short tail
Yes, but slowly.
A fantail goldfish can be any of the goldfish colours which can include any or all of the following white, gold, silver, copper, blue, orange etc etc.
Survival of the fittest
suma nimo
Became a coluar
They are both goldfish and so can breed with one another if they are of different sexes.