Get one or two professional opinions. Find out the pros and cons of doing it now or after kids. You will ultimately have to make the decision.

It's hard to do anything when you're carrying around alot of breast weight. And it's probably not great for your back.

I had a breast reduction when I was 21 and was told that there was a 50/50 chance I might still be able to breast feed. I had a child prior to the breast reduction and one after. With my second child I didn't have any signs of milk coming in. If you are really set on breast feeding, I would hold off on the reduction, however, there are many other healthy alternatives to breast feeding available.
I noticed a huge difference after having my reduction. I even managed to be 2 inches taller because I was finally standing up straight! I would have the reduction again in a second. The recovery process is not pleasant but the outcome definaltely is worth it. Hope this helps.