Like everyone said, it depends.
For the Goofy last year I wore a throwaway sweat suit to the start but shed that before we started. I wore the same stuff for the full and the half.
Visor (more for keeping sweat out of my eyes), sleeveless shirt and shorts. To keep warm for the first few miles I wear $1 gloves from Home Depot and arm warmers. For the arm warmers I bought tube socks and cut the toes out of them. They were great for the first few miles and I could just toss them once I got warm enough. Although I wore them for the entire half.
Probably go the same this year. If it is much colder I might wear a throw away long sleeve shirt.
For the LV race a few weeks ago, where the temps were in the high 30's I wore a lot more. So, if Disney is that cold I'd pretty much wear the same items. I had on shorts and long sleeve running shirt, running pants, not tights, running jacket then a throwaway jacket over that. Gloves, hat and ear band thing to keep my ears warm.
I ended up wearing the running pants, extra jacket, gloves and ear warmer the entire race. I did unzip the jacket in the last couple of miles so the photographers could see my bib
enjoy,
Duane