We brought our 4 month old to WDW in Feb year before last. I was not prepared for how cold it would be and only had light weight blankets. That was our only problem. He pretty much lived in the front pack (Baby Bjorn is a beautiful thing!) I fed him on some of the rides--nursing very discreetly. And he slept on and off varied with looking about simply amazed. Since we have taken kids at 1.5, 2.3. 4, 5, and 6, I have decided that the baby was the easiest one. (Though all ages have their merits! Ranging from Joy and wonder to self sufficiency.) You will have a wonderful time. And if the baby is your only one, your life is much more flexible if he/she will sleep in a stroller or front pack/sling. YOu can stay out late while baby sleeps! By the way, bring your own stroller. Those plastic jobbies do not work for the little ones.
Or better yet, rent one from A Baby's Best Friend. They are the greatest!