First they often shiver right after waking up, in order to raise their body temperatures. Second, they shake or quiver when excited or frightened. For a young kit, this could be all the time, since everything is new and interesting. For older ferrets, a bath or even a good scolding could prompt trembling. Most often, yes.
Ferrets sleep quite a bit, even adults.
Ferrets sometimes appear to be sleeping with their eyes partly open, and they sleep very heavily, often not waking even when picked up. Ferrets will readily adapt to your schedule, however, and if you let them out to play at certain times everyday, they will adjust so their playtime matches yours. Ferrets are very sociable animals. They will become attached to you, and will suffer if not handled and played with on a daily basis. Ferrets are not like a hamster or gerbil.