My husband wanted 3 and I did as well until both my mother and sister shared the following vision of the future with me. It's so easy right now to think that having a 3rd will round out your family but consider the following:
Your husband will be working while you are taking care of the kids, you have two hands to hold two children...a third is a juggle and when one goes running into a crowd of people, you can't just leave the other two behind.
Wait until you start sports, homework, school field trips, vacations, camping, making school lunches, back-to-school shopping, flying on planes with all 3 kids, all the extracurricular activities. Besides the obvious expense of having another child, you will not get much down time to yourself....at all! Your weekends will be filled with a full day of soccer on Saturdays, soccer practices for each child...or baseball, drama whatever they're into. Your evenings will be filled with helping all 3 children with homework, shuttling them to and from their friends houses, school and practices. If they play an instrument...you'll be sitting with all of them after school helping them practice because they can not do it alone.
The amount of noise, mess, fighting and chaos will create more stress between you and your husband as you'll both be yelling a lot...and you won't have time to read all the child behavior books to figure out how to deal with it.
Let's talk about your sex life...getting time alone will be very challenging. Then there is the flu season, when you get sick...you still have to take care of all 3 kids and drive them to all their activities. Story time at night....you can easily divide up between two parents with two kids so they each get one-on-one time.
Then there's college to think about (3 private college tuitions...have you seen what the tuition is these days? It will only keep going up).
Most of the women I see with 3 kids look very tired unless there is a full time nanny in the house.
Then there is the possibility of divorce or death of a spouse...it is very difficult to find another mate who will want to take on 3 step kids....two maybe.
All food for thought. My sister, who is 8 years older than I shared this same advice with me when I considered having a 3rd. I'm so grateful to her now. Sticking with two was the best decision my husband and I could have ever made.
Just food for thought. Good luck with your decision