Having more than one cat indoors is a good way to keep them
from going nuts. If one comes in as a kitten to an adult cat,
you probably won't have a serious problem over pecking order,
and the adult will probably 'adopt' the kitten.

One of our cats tends to spend a lot of time with me alone
at my place (he likes to ride in the car anyway) and he is
a lot more 'needy' of human companionship when he's away
from the three other felines. In the 'pride' he's the 'top cat,'
and a bit more aloof from people. Away from them, he wants
lots of attention and play from his humans.