you will need a gallon for every inch the shubunkins grow
you will need at least one gallon for a snail
Neon tetras, guppies, and bettas are warm water fish(they need a heater) and calico ryukins and shubunkins are cold water(don't need a heater) so none would really fit together except the warm waters. I have a shubunkin goldfish, common goldfish, and 2 dojo/weather loaches in a 29gal, but they used to be in a 10gal. I recommend another double tailed goldfish if you have the ryukin(single tailed will be faster and nip at the others fins and eat all of the food).
goldfish need to lay eggs. Because if they don't no goldfish would be alive and would not be any more so they would become gone forever.
bottom feeders (sucker fish). i used to have one, it ate my water snail + they don't need to be in groups and they are about the size of a goldfish.
there are three basic breeds: fantail goldfish, comet goldfish, and common goldfish. if you are getting goldfish for the first time, i would recommend common goldfish as they need the least care.
you need to have a gallon for every inch they are
That would normally be a pet shop, but to get a female goldfish you would need to go to a pet shop specializing in fish, and have them determine which were female.
they can live in goldfish bowls i have always kept my beta in a goldfish bowl and my last beta lived between 4-5 years in a goldfish bowl.
A swordtail is a tropical fish and a goldfish is not. The swordtail would need a higher temp. than the goldfish. Depending on where you live it probably wouldn't survive the winter.
That you need a new goldfish
No
Yes,snails can have a family and the snail don't need to mate with another snail
Green peas are rich in fiber which is good for goldfish. The only thing is, with canned peas, I would be sure to rinse them thoroughly in water. The goldfish do not need the preservatives and salt that might be included in the canning process,