Congratulations!!!!! Seth is adorable and I love that last picture you posted of the three of you with the nurse in the background. My Ellie was 5 lbs, 15 oz at birth and 19.5 inches so very close in size. We were in Newborn clothes for a good 6-8 weeks, then started the 0-3 months and was quickly in 3 months clothes after that. Just thought I would let you know - we ended up needing to borrow a few Newborn items from friends. She did wear Preemie clothes for about 2 weeks, too, that we borrowed from a friend.
You all are such a cute family
PS - that was a very quick labor for your first! It was almost the same as my labor with Ellie, I was 5 cent when I got to the hospital, but water broke at the hospital right after checking in, then she was born 2 hours later. It is so funny how many similarities there are.