Well- when I was young we had two- they earn as said by the AKC as the "clowns of the setters".. I am concerned in not only the size difference, but any large breed stays a puppy longer than a small one- with all the klutz etc associated. ( including my own..) In general it takes two years if not a little more for the large breeds to grow up. That means- no clue how big they are, how to stop from crashing into things etc. And anytime you have the size difference, you have to protect the smaller ones from being " accedently run over " in the yard. Just as I have to protect my pups from being run over by the adults, you would have the opposite in protecting the smaller adults from and exhuberant puppy. I know you have a fenced area to let the puppy run as setters love to run.
As long as Hubby is willing to put the work in to bring the pup along until adulthood- it should be fine- but it does take daily diligence to bring in any dog that would have a big size difference. Also remember- terriers in general think they are a " big dog" and some even without the clue they are as little as they are. I know when I had my affenpincher Crikket with my Dane Lilly- it was a constant supervision- in and out of the house! Big paws do not mean to step on things- but they do.. Zubin and Galina are getting close to two years old- as you know- they still see themselves as puppies- and its not just because there are two of them- they really do even when seperated. " When in doubt- run to something- and worry about stopping when you get there..." lol..
As far as setters- as a trainer- I have found the Gordons and the English more sensible. I love - TO THE POINT OF ADORE- the looks of the Irish, but the other two breeds really are more sensible and sensitve to their surroundings. Also keep in mind- all 3 of the setters need daily brushings with a pin brush.
I am not trying to talk you out of this Jo- you know that- I am just tossing out things for you to consider BEFORE bringing that adorable puppy home. Remember- not all breeds work for all people. Neither of my two setters were chewers- but they had alot of exercise daily.. Alot! As I would say to anyone getting a big dog- keep in mind- do you really have the time for the morning run, and late afternoon run or dinnertime run. A high energy breed needs daily exercise- not excessive for growing bones and joints- so several short runs a day is better than one long one. Being good hunters- they are independant minded, and never should be outside a fenced in area to run loose as they will follow a trail..
All just thoughts for you to consider.. WE have known each other long enough for me to be honest here- knowing you will consider what I have said as an attempt to help with decissions before the puppy comes to your home.