I think you might want to pack expecting warm days and cool evenings. I know that you don't want to pack TOO much, but the weather here in Florida is unpredictable, as it is in Ohio (I live in Florida now, but I've lived several years in Ohio too). I'm visiting WDW myself next month (March 17-20), and will take along a jacket, perhaps even a long sleeve shirt, but I'll also take along shorts and short sleeve shirts. (And, for me, a hat is nice to have along. Keeps the sun and rain off the face a bit.)
If it's cold in the early morning, and you later get tired of lugging a jacket, sweat shirt, or sweater around as the temp raises in the afternoon - remember that all four parks have storage lockers you may use if you want. Then, if you stay late, as the sun goes down, and it starts getting a bit cold, stop by your locker and get the jackets back out.
Since it may well rain while y'all are in a park I would advise packing two pairs of shoes for each person in your group. That way you will have a spare dry pair waiting in your room for the next day's doings.
Enjoy.