I think you've picked a really good time to go with a toddler. My memory from our 2000 trip with 13mo DGS is that WDW is actually not very toddler-friendly. Lots of places it's hard to maneuver the stroller, and lots of places you have to leave it parked a lot sooner than I would have liked to (that might not be such a problem with the reduced crowds you'll have). DGS is one of those fearless, quick wanderer types, so we used a leash fairly often -- some people give you strange looks about those, but the extra peace of mind is worth it. There are tons of distractions at WDW. We ended up using the car most of the time, to save the hassle of getting on and off busses with the stroller. Ease the young one into character encounters -- don't force them, let her set the pace. The TTA in MK is great, sometimes you can ride it around several times, with napping baby.
Too bad it will probably be too cool for Typhoon Lagoon -- that was great. I went around Lazy River 3-4 times with DGS napping on my lap in the tube.
Prepare for all your creature comforts -- ponchos, stroller cover, first aid, diapers, drinks, etc. Don't expect to do it all; take it easy and enjoy.