Coming from NY, expect late October, Early-April-like weather. You know how it could be either 70 degrees in October/April or 50 degrees and chilly? It's exactly like that.
In 2009, there was a serious cold front. It never got over 55 degrees and at night it dipped into the 30s. The next year it was warmer, with a few days in the high 50s - which meant nights in the low 40s/high 30s. Our best and most consistent year was 2013. It stayed warm pretty much all trip, hovering in the 70s, with one or two cooler nights. Last year it made it into the 80s some days (it felt hotter). We wore shorts and t-shirts those days. At the end of our trip, it got rainy and cooled down substantially - 60s, low 70s and damp at night.
I'd do layers. I pack for fall/early spring. Long-sleeve tees, jeans, a light hoodie, etc. Then, I pack layers. I pack sweaters and sweatshirts. If it's cooler out one day, I'll wear a long-sleeve shirt with a hoodie. I also pack some collared shirts for dinners. I then pack for extreme temps. I pack short-sleeve tees if it's hot out (I sleep in t-shirts too, so that helps.) I also pack two pairs of shorts that go with anything. Then, I wear a winter coat down, bring gloves, a scarf, thick socks and a sock hat. I play around with layers depending on the temp. Also - hand warmers. Haven't used them the past two years, but wish I had them the previous few years.
Remember - you're surrounded by water. EPCOT and MK always feel a bit chillier and the dampness can make it feel about 5 degrees colder.