Hi Ben,
You will get a LOT of great info here - and that does not mean that mine is by any means more valuable than some of the others as there are wonderful and well educated and very invloved breeders on this forum so you are in the right place.
1st - have the parents been shown to thier championship?
2nd - Have they done the proper health screening? You can swap question # 2 in for a tie with question # 1 .....
3rd - were the parents well tempermented? again, I think temperment is equal in importance to question 1 & 2.
4th - is he balanced and well put together over all?
5th - how big is mom?
How many puppies are there, and are you taking home the largest?

I would not worry as much about size as long as the breeder is ethical, breeds for sound temperments and has thier health certified.
there are several other things you may consider - depending on what is individauly specific to you and what kind of relationship you have with your breeder.
THere may be people on here who know more about the breeder, and you will get a great deal of information......If you are buying a pet and the are "good people" you will not be dissapointed - but cross your t's and dot your eye's and gather info.
Luck

Melissa