In terms of the breast reduction, I agree for the most part with what has been written by my colleagues, specifically to wait a few months after you have completed breast feeding before considering a breast reduction. It's important to remember, however, that breast reduction surgery does have some inherent risks, including losing sensation to the nipples and possibly losing the ability to breast feed in the future. So when you are considering this procedure, it's important to ask yourself if this matters to you or not, and to have a very thorough discussion with your surgeon about the advantages and disadvantages of the procedure.
The part of your story that I also wanted to comment on was the possibility of having a tummy tuck at age 17-18. It's important to understand that while a tummy tuck can really give you a wonderful improvement to the appearance of your abs, this look will completely change should you become pregnant again, which given how young you are, is certainly a possibility. My advice for women considering a tummy tuck is that in most cases (not all, but most) the best option is to wait until you have had all of your children, and then have one procedure that will last for years to come.