Here's my advice:
If you can get your formula in powdered form then bring that premeasured to the park. Carry a room temp bottle water and mix when needed. Try if you can to get the baby use to room temp bottles before you go. It might not work and if not don't worry. Use the baby care centers in each park. They are wonderful. There is a room for your older child with kid sized tables and chairs and tv with movies. They have a kitchen with a CM there to help you purchase things orhelp with anything else. There is a stove, micro, fridge and endless supplies. For sale is anything you could possibly need for a baby. They also have a water cooler and gummies to buy for your older child. They have seperate rooms to privately nurse babies. They have highchairs and a co-ed bathroom. A large changing area equiped with a sink and large changing tables. The whole family can go in, you just can't bring in the stroller. We used these everytime DS, 8mo needed a bottle.
Definately bring your own stroller. Your baby will be much more comfortable and you'll need it around the resort. Another must have for me was the Baby Bjorn carrier. It never hurt my back and it gave my son a break from the stroller. Don't forget to put a hat on the baby. Ask your Dr. about sunscreen. The sun is still strong in the winter. Take your time and maybe seperate and enjoy a quiet bench and people watch while mom or dad take your older child on an attraction. We did this on our trip in Nov. DD was almost 6yo and DS was 8mo. I find that taking an infant is really easy. They sleep alot and all you have to do is feed them and their happy!!! They kinda forse you to relax and appreciate the little things. For example, one of my best memories from our last trip is sitting on a bench shaded by a tree in Epcot with my son asleep in my arms while I watched DH and DD play on the Viking ship.
Good luck and relax, you will have a great time!
Any other questions, just ask.