We just took our guys two weeks after they turned two. *I* thought it was a successful trip, though DH may beg to differ. (Though he also doesn't spend ALL day long with them like I do, and just prior to our trip, he had pretty much been gone for a month so I don't think he really understood that the terrible twos had indeed come on schedule!

) But anyways-- especially if he's still taking an afternoon nap, I recommend you get there at rope drop, have an early lunch, and be back at the resort for his typical nap time. We only had one massive melt down and it was the day we stayed just slightly too late. Use fast passes too, but especially if you're there at rope drop, you'll be able to get in plenty of things WITHOUT standing in line. I don't think we stood in line longer than 15 minutes, most of the time it was far less than that (we were there Apr 19-24.)
My guys were over 36" tall and slept fine in Pack n Plays, but all kids are different... And we drove, so I can't help w/ the car seat either.
The boys favorite ride by far- was the boat ride in Mexico w/ Donald Duck. I don't know why exactly, but they both loved that one. (they STILL are talking about it weeks later!) One twin did not care for rides, poor thing would bury his head into our chest even on IASWA!! (Though after being on it for a few minutes he warmed up.) They liked the Winnie the Pooh ride as well. The other twin, however LOVED all the rides, had a fit when Dumbo was over and asked to ride Goofy's Barnstormer a second time!!

So again, kids are different, you'll just have to see! Though my brave one didn't care for any of the shows if they got dark- Philharmagic made him jump and turn around when the lights went out. The little play ground across from Winnie the Pooh- Pooh's playful spot- is great at this age. The boys really enjoyed that, and thankfully it's for the smaller ones and there weren't really too many bigger kids causing ruckus.
If I could do one thing differently, I'd have taken them to more character meet and greets- they LOVED the characters!!! Though the downside of that is when eating at places like CP, they could see all the characters walking around the room, so they were so excited, they didn't eat a bite, then got really upset when the characters only stayed long enough to take a picture.

(for character meals, I recommend the Garden Grill BY FAR- best interaction we had the entire trip!)
Anyways, go and have a great time!!!