Greeh, I didn't really answer your question, did I? I have added stray kittens to my cat family to cats as old as 11, but not older. It really depends on the individual cat. Kittens love to play, and mine were well accepted by my younger cats, who also liked to play. The oldest cat was "above all of that kid stuff." She liked me to play with her, but didn't like to play fight. Kittens do.
I wish I could give you more help. I have had problems with only one cat since I became an adult, and I have never turned a stray away. The one cat was a bully, although she was (we guessed) only 6-7 months old. She intimidated our most sensitive cat. That was only one of many. I'm sure Ben would know that he is the Alpha Kitty. If you get the kitten, (and I'd be tempted) I would use interactive toys to keep him busy. He will miss having his litter mates to wrestle with, but Ben would teach him a lot, as his mother would.
If you get a kitten, I would consider one that is rather laid back. You mentioned a Snowshoe Siamese. As I mentioned, I have Siamese cats, and find them to be very loving. But, just as we are individuals, so are cats.
I hope that helps a bit, and that others tell you their experiences.