I only have one ferret but I spend a lot of time with her so most of the time I would say to get 2 or more. More fun to watch too.
I couldn't tell you about the "better" sex but females are normally smaller with a lighter smell and males are normally larger with slightly stronger scent. Mines a female.
I don't think they would need to be litter mates but if you get around the same age then they seem to accept each other easier.
Most young ferrets (kits) are very wiggly and don't like to be held much. The older they get the more they allow you to hold them. I would say they are cuddly when they want to be but when they want down it's time to let them down!
I give my girl about 4 to 5 hours a day (hr before work and then 3-4 hrs after work). That's all they "need" but will take all the out time they can get.
Ferrets normally will get to where they will use the
litter box fairly often even outside the cage. Mine has about a 80% hit rate outside. Mistakes will happen though!
Stinky likes to be held when she's sleeply. Otherwise she wants to play. She will seek me out when she wants to be held and loved on.
I think I got most of your questions. Good luck!
