Your little pup is missing his litter mates and the only family that he has known, so it is quite natural for him to be upset.
 
Try a radio beside his bed or a small ticking clock.
 
He will soon be ok and used to the situation.
 
He can live outside as soon as you wish, but around 10 weeks should be ok. Make sure that he has pleanty of warmth though.
 
He and the cat will sort things out pretty quickly. Usually the cat ends up as "boss".
 
cheers,
 
Jack