Yes
(I keep fish too :P)
No, that is only about 6 gallons; fancy goldfish need at least 15 gallons each regardless of how tiny they seem when you buy them
Tetras look great in schools of 8 so I'm guessing tetras are the best in groups, however there are also fancy goldfish for individual beauty. Hope this helps -goldfish keeper
an aquarium or a fish tank
Comet goldfish grow to be around a foot long. 120 liters is about 30 gallons so I say about 2. Get fancy goldfish because you could do even five in a tank that size because they don't get as big.
25
Bettas livebearers goldfish cichlids saltwaters
Yes, for they are both Fancy Goldfish (It's bad to keep Comets with Fancy varities because most likely the comet will become stressed and die).
Goldfish may be kept in an uheated fresh-water aquarium. They are considered ill-suited to live in a heated tropical fish tank, as they are used to the greater amount of oxygen in unheated tanks.
If you arent going to do regular maintenance, keep it to 5 or less godlfish.
Keeping the water clean in your goldfish aquarium will not only make your fish more likely to spawn but will also greatly improve the health of your fish and any potential fry, so yes you should keep your goldfish's water clean for them to spawn.
Tropical fish are normally kept in a heated aquarium. Goldfish (and similar species) are usually kept in a coldwater aquarium, or in a goldfish bowl. Where fish are reared commercially for eating: salmon, trout, etc. they are kept in floating fish hatcheries that are usually found in Scottish sea-lochs.
I would personally say none, not for their entire lives anyway. You may get away with 2 Fancy Goldfish juveniles for a couple of months, but really Fancy Goldfish need a minimum of 20 gallons each and Common/Comet Goldfish a minimum of 55 gallons each for their entire lives! They get very big, are very messy and need a lot of water volume!