If you can and have enough money you should definitely get Two. Some ferrets can lonely and stressed if things to do a day and another ferret friend can give both ferrets exercise and comfort. if you spend the day at work or school the ferrets need each other and get very attached!!!!
Not necessarily. As pets, you can keep one, and it will be perfectly content if you have plenty of time to play with your ferret as they crave human interaction, two can keep each other occupied if you don't have a lot of time for your ferret.
So the answer to your question is: 'No, they don't have to be in pairs - but they would prefer it.'
Yes - if they're already friends. Two ferrets provide company for one another. Our two constantly snuggle and play together and one on its own would need more attention from us. However, buying two ferrets who do not know or like one another needs more care.
Ferrets are not pack animals. But, due to domestication, they retain more juvenile characteristics (cf.s dogs similar behaviour to wolf puppies). They view their companion ferret as a litter-mate.
Yes, ferrets do like to be in pairs but they can be just as happy by themselves. If you are someone who is busy and can't let your ferret out of the cage as much as you are supposed to then you should consider getting another ferret. But you still have to remember that even if you have two ferrets, they still have to be let out to run around and play together. Even if you are thinking about getting another ferret you also have to remember that you may have a ferret that may not get along with another ferret so you may be his only friend.