Oh how much fun you'll have!
My youngest is now 3 but has been to WDW twice already; her brothers have been a few more times on top of that.
My advice -- be leisurely. Kids that age sense when they are being pushed along (and don't like it!) Besides, in a few years, he'll be dragging you all over the place and YOU will want the afternoon nap!
This is your chance to see Disney through the eyes of your child -- that in and of itself is the best "ride" in any park, ever!
So advice: Strollers. If you don't mind bringing yours, I would -- I love the Disney strollers, but they are increasingly lacking in any storage space, and for a napping child, they don't recline. If you don't intend to nap on the go, then I suggest bringing a small bungee cord and packpack for the essentials -- we attach it to the side of the Disney stroller (if you attach it to the back, it will tip the whole thing over...). Your own stroller also gets you to/from the WDW transportation... after lugging our sons back and forth to the buses a few times, we wished we had strollers for dh and I as well as our boys, too!!
Essentials: light snacks and juice. If you will have access to a fridge or freezer, freeze a few juice boxes. Light snacks like cereals and typical toddler fare is all good stuff. They can munch this while waiting in lines. Chances are very good that they will be too wound to eat if you stop at a restaurant, anyway. Everything is so... stimulating to them! That's one really nice thing about going back to resort at lunch time. It gives some much needed escape from the hoopla. They will actually rest better at night, I think! Leave park at about noon, come back at 2:30 just in time for parade... your child will be the one sitting happily in his stroller, fresh and rested, while around him the tired and weary wail. Or skip the parade and let your child enjoy the characters at Toontown or his favorite ride without any wait!
Push lots of fluids -- they dehydrate quick, and May can be quite warm! My kids just never fared well on the Florida water -- that's a whole topic in and of itself. If you aren't sure how your child responds to other water systems, use bottled water. And because tummy upsets can be part of the turf with kids and large parks, always pack an extra outfit in the ol' bag and plastic bags for any "dirties". A wet washcloth can work wonders on a tired hot child (and sticky ice cream hands). Sunscreen, of course, and maybe a clip-on stroller fan (like the kinds from Right Start or similar company that are baby-safe -- blades stop if they stick a finger in them). We never had too much issue with bugs...(despite the fact that my dd is a mosquito magnet). Many bug sprays aren't for use on kids under 3... you can try a bit of Avon SSS.
Just a few ideas... I won't necessarily suggest what to see because (a) it's so child dependent and (b) it's all so good!
Best restaurants we've been to with kids is changing for us as ours get older, but the Pooh character b'fast is always good for the kids (Pooh is fairly well accepted by most small children, although my son had an extreme fear of Eeyore at age 2! Fortunately, Eeyore just stood back and waved sadly at a distance!) I'd also suggest Chef Mickey's. In Epcot, Garden Grille was good and our boys loved Teppanyaki (although dd, then aged 9 mos, slept through it all!) We tend to prefer the buffet type meals at WDW because when our kids were small, it meant food right away, and we could just get them a bit of this, a bit of that. And now that they are older, they enjoy going up to the buffet and selecting what they want for themselves. It's just so much easier that way! You might want to look at off-peak dining times since if your child isn't well-rested, it won't be as long a wait or as hustle-bustle in the eatery. (Another reason for bringing along those snacks...)
Just a few ideas....
Cindy