Thanks. I did read those (I'd seen them on another post of yours and they are good).
I should clarify I think Sasha is pretty well socialized now (amazingly so, given his lack in puppyhood), but the things I mention are really just personality things and to be honest not even things I'd necessarily want to change. I mean, yes, the dog will hop down off the couch when my dh walks in to sit and wait for him to sit before hopping back up (and will only hop up if I tap the seat), but he also won't go up/down stairs before anyone in the family or through doorways or even THINK of pulling on the lead on a walk (funny considering the first time I put one on he acted like a cat, but a weekend away from home and he just started heeling perfectly). My 9yo loves taking him for daily walks, and he gets so excited it's hard to get his harness on!
I mean, you'd THINK he was the best trained dog EVER, but it's just a complete lack of any dominance issues. He is a very calm and relaxed dog because he trusts "his pack" now and is happy "on the bottom". He is playful and enjoys the kids, and the only time he challenges anyone is he will try to steal pieces of cheese sticks from the youngest if he gets a chance. Of course, this doesn't stop him from going crazy if he gets hold of a piece of kleenex.
So the thing with dh I think is some sort of male-male deference I'm hoping might ease if we get Sasha neutered (we delayed it for health and then also for mood, esp while he adapted to our home).
My concerns would be more that Sasha will be pushed around or feel left aside. A new puppy would have an unknown personality and might not have Sasha's easy-going dominance-free personality. One of the reason we're considering a puppy is for the kids to get the experience and training, and because a family member is getting one of the litter, so they will be visiting frequently. It's kind of now or wait at least 2 years. Of course, in 2 years, our oldest would be old enough to get up with a puppy at night.
ETA: All that to say, what I am really interested in is what other people's experiences have been. I guess what I am really wondering is whether the age of the first dog matters and whether companion breeds like havanese are any different about adapting to a new dog than a dog bred as a working dog, say a retriever or terrier?