Tummy tuck should not be confused with liposuction or as a weight-reducing procedure. It mainly focuses on the weak muscles and the excess skin that can be difficult to achieve through an ordinary exercise or a simple diet. A horizontal incision is made above the pubic area where excess skin and fat are removed. Then the muscles will be lifted and repositioned, after which they will be sutured together tightly. The navel position will definitely be altered since the tissue connecting it to the wall is removed. You should try to get maximum info before deciding anything. I have found related useful info at: http://www.plasticsurgeryace.com/category/tummy-tuck
I recommend waiting as well! you are also young...
I would recommend waiting until after you have all your kids before getting a tummy tuck. I got one after having 2 kids. I was much like you after the 1st kid, but since I wanted another kid, I didn't want to pay for the surgery twice. After a tummy tuck, your tummy is very tight. If you get pregnant after a tummy tuck, you may experience a lot of pain while your belly is growing. Esp. since you want other things besides a tummy tuck, i say wait.