We traveled overseas when my DS was about 4 months old. We did bring a stroller and just gate-checked it before boarding the plane. I know that Disney rents out strollers, but you will probably want your own for times when you are not at the parks.
Other items such as diapers, wipes, etc....I would bring enough for a couple of days (including flight travel time) and buy the rest when you get there. If you are renting a car, you can easily find a pharmacy or grocery store to buy these items. If not renting a car, you can take a taxi or possibly a shuttle bus. I find it much easier to buy things when I get there versus packing a million suitcases full of baby items.
For the plane ride, your baby will be so young that s/he will likely sleep for much of the flight. Will you be nursing? I found that really easy and comforting for my son while on flights. If not, make sure to bring plenty of bottles/formula and pacifiers if your child will be using one. You should also bring a couple of new toys, some changes of clothes and OVER estimate the amt of diapers and wipes you would need for the day(s) of travel.
Hope that helps!