For us, there's the concern about finances for sure! I also wonder how a third will impact the two I have. I've heard that with three, two sometimes gang up on the third, with the third one feeling left out. With all the losses in my girls' lives, I don't want to do that to them. I am concerned about how much I can handle--especially when we travel. We want to travel with our children and show them things, but how many can we have and still reasonably do this? And then there's the concern about upsetting the good family we have formed. What if we adopt a child with RAD or some other problem? I know that was always a possibility, but we have been so lucky, and every leap of faith is one more chance of having a child with real problems. Still, I can't help this nagging feeling that we should adopt again. In fact, I somehow envision three girls and a boy, for some reason. I don't know why I picture this since DH would never agree to a fourth!
For us, we decided to put the decision on hold and wait and see. It's my belief (just mine) that God will put us on the same page. Either DH will decide a third is the way to go, or I will decide that two is enough. I can say that it IS nice to get to the stage where there's no more potty training,and the girls can travel and start to remember trips. We're definitely in a comfort zone.
I have other reasons for considering a third, but they are reasons that wouldn't be universal to everyone.
Anyway, I have zero advice for you. I just wanted you to know that you aren't alone in your situation.