Ahhh 1st post got eaten...
We are taking our 4th in Oct and he will be 5 months. We took our other kids from about 3 months on and they did great...I think they are better 12monts and under than at 2-3-4!
Somethings to conisder, if you do table service restruants will your baby be able to sit up in a wooden restruant highchair? You are not able to take a stroller into any if not all of the resturants, Counter services are fine with strollers though. The reason I ask is that our babies did not like being in the car seat for long streaches, they were cramped and hot so we would just have them in the stroller reclined. Leaving the car seat in the car... But then where to do put them if they can't sit up?
Consider getting Medela Micro-Steam bags for cleaning and saintizing bottles, nipples, pacifiers, breast pump parts etc.., you can use one bag 20x so I would pack one and at the end of each night would go to the foot court area to clean what we used that day they take 2 oz of water and about 3min in the mircowave dependeding on wattage. At ASMo I belive it was 90 sec based on that mircowaves wattage. Instrucitons are on the bag.
If you or your wife nurses get a hooter hider. I nursed our babies all over the parks and would take advantage of a shady area with a bench. My privacy was intact, baby was eating and no one else was uncomfortable beacuse we were covered. I also, like the OP said nursed on dark rides cool and dark.
Try a baby carrier, we used to use the Baby Bjorn but have now learned about the hip displacement/spine problems. We now use a Moby style baby wrap in a mesh UVA/UVB safe fabric that is light weight for the parent and the baby.
Condider a larger sun shade if your stroller doesn't have a big one. Consider a rain cover for your stroller, I have scene families try the rain poncho and binder clip set up but is donsn't work for long and not with some wind. Our kids are high and dry with ours, we put it on the stroller at the begining of the day but roll it back. While on/in rides and attractions we cover our stroller for pop up rain showers. Also keeps our stuff dry.
Bring your own pack and play sheets and have your baby sleep with his/her favorite blanket and sheet for two nights before you leave to have the smell of home on them.
We also got a small battery powered fan and some velcro tape to put a fan in the stroller, worked great for about 6.00 total. The stroller fan's at Babies R Us were like 25.00.
If flying ship diapers, extra bottle, formual wipes etc two weeks before you leave to lessen you load and suitcase space.
Take an extra onise style outfit EVERY into the parks, save youself the trip back to the hotel if a diaper blows out or spit up.
Try you babies sunscreen on a small part of skin before leaving to make sure no reaction occures. Our Ped told us to use Califorina Baby sunscreen on babies less than 6 months (got from drugstore.com).
If I think of anything else will post againg. I hate to pack a lot of extra crap, these are the things I really think are worth for a sunny/ rainy WDW trip with a baby.