If it is kept clean.
yes
Small or Big it should be kept in a huge tank with Filter and Oxygen 10 gallons per Goldfish At least
if you have a very aggressive betta fish, placing them with any kind of crab is probably not the best idea. Crabs, even if they are mostly non-aggressive, can rip a betta's long tail and fins to pieces! Bettas could also bother the crab, and then you have a full blown fight on your hands! If you really want to put them together though, watch them carefully for any signs of aggression.
Goldfish (Carassius auratus) are small ornamental freshwater fish that are commonly kept as pets. Goldfish were originally domesticated from the Prussian carp (Carassius gibelio), a dark greyish brown carp native to Asia. It was first bred for color in China over 1,000 years ago. Due to selective breeding, goldfish have been developed into many distinct breeds and are now found in various colors, color patterns, forms and sizes far different from those of the original domesticated carp.
no
Yes they can
There is no record kept of the "oldest Goldfish" but I have known them to live for over 20 years.
The goldfish should never be in the same tank as guppies. Goldfish are coldwater fish and need to be kept below 70F. Guppies are tropical fish and need to be kept above 70F.
No, freshwater fish must be kept in freshwater and saltwater fish must be kept in saltwater. The one exception (that I know of) in nature is salmon which migrate from where they were born (freshwater) to the ocean and then back to where they were born again to breed.
Mollies are tropical fish and should be kept above 70F. Goldfish are coldwater fish and should be kept below 70F. They should NEVER be kept together.
Though this is not an EXACT estimate, Goldfish, if kept in a outdoor pond, will hibernate from November/December to February.