Hi
Actually I think is more than fair. Your little guy you have now would have a playmate when you guys are kinda busy or at work etc.We just got a little pup to be with our year and a half old yorkie and when we go out I feel he has some company. He seems to enjoy him Our older one also is teaching the little guy to go potty outside which is nice.
It sure would be easier now than in a couple of years when you have a new baby. The new pup would be all trained etc.Also your little guy would be that much older and maybe not into the puppy play as much.
But that is just my opinion and it is just what your comfort levels are. You have a lot on your plate for sure so guess you have to think hard about it...Good luck with your decision.
Take care