Def. when you get there start small, carousel....dumbo...
Yes yes yes.
Start with OUTDOOR rides, the ones when you can see just about everything. So Dumbo is GOOD. Carrousel is GOOD. Peter Pan, even though it's awesome, is BAD, because it's inside, and the queue is dark (might not seem dark to an adult, but to a little kid it can, which is what counts).
We LOVE DCA's bug's land for the first bit of a trip! NOT "tough to be a bug" (omg no), but the actual ride-rides. Heimlich's Chew Chew Train involves burping! Hilarious to a 3 year old. (and 7 year old. and 40 year old husband. and, ok, to me too) Flik's Flyers yay! It's a great place to hang out for a few hours, bring the bathing suit and sandals (along with a towel and dry clothes), let him play in the water spray areas, ride some rides, just have a GREAT time in there. It's a good way to ramp up to more rides.
Snow White and Pinochio should be OFF the list. 100%. Peter Pan can be worked up to. Alice in Wonderland is freaky, and I don't recommend it for a skittish kid. It's a freaky book, and a freaky ride.
Storybookland Canal boats is great, but you go into the mouth of Monstro (who can be seen from the outside), and it took DS until this last trip to be happy with that.
Casey Jr is really fun.
Once he gets used to the outdoor stuff, that's when you start with the indoor fun stuff like Pooh. Slowly slowly.
DS went to
Disneyland at 17 months then a year later, and was fine with everything, then we went once or twice when he was 3 and he HATED EVERYTHING. 3 was his year to be scared. So we adapted. Then at 4, when we went for his birthday, it all opened back up to him again! Pirates was great again, and so was Peter Pan, etc etc.
The "whims" of a 3 year old aren't really whims to him, they are powerful emotions as he goes from toddlerhood (where the reality of things isn't quite real yet) to young childhood (where differentiation between real and pretend gets easier), and he's stuck in a place where everything seems really very real, and if something is scary, then it's scary in reality. So don't cancel your trip, but take the little dude seriously. It's his little brain that's dealing with this, so help him along.
EAr protection is wonderful! I can't recall if it was DS's 4 year old or 5 year old trip, but during one of them I finally realized just how LOUD the whole place is. Rides, yes, queues yes, loud loud loud. But just the ambient noise is very loud! We were standing in Tomorrowland having some other issues (involving having forgotten to eat for 9 hours) and I remembered I had my earplugs in my purse and I stuck them in DS's ears. The tantrum level came down by half just by shutting off a lot of the sound. (if only I'd had some for DH, who was tantrumming right back at the kidlet)
The place is loud and you'll do him and your family a big favor by being prepared for that.
From our experience, I wouldn't recommend Nemo as being the first ride of the day, because of the loudness of it. Our ears were ALL hurting the time we did that.
Umm, I would think about skipping the cologne and just using water or glitter water, even better. What if he gets scared in a restaurant? Or sprays near someone allergic to such things?
I actually wear smelly stuff, but not all the time, because sometimes I can be allergic even to the stuff I wear! (it's not fun when I don't realize I'm in an allergy mode and have sprayed myself...I spray in the air in my bedroom then shake my hair through the cloud, so it's HARD to get the smell off of me if I realized I'm sneezing)
So along with larina, I do NOT recommend putting the stuff into cologne. The theory is good, but needs to be refined so that it's not harming or annoying others.
I would also suggest that it's also a lot of fun just to walk around the park, look into shops, etc, without even going onto one of the attractions. Don't get me wrong, I love the attractions - but it might ease him into what's going on. He might even be the one who suggests you go on one of the attractions.
Yes yes, good point!
My kid can forgo lots of treats if he really doesn't want to do something. But the one thing that has worked, over time (not immediately usually), is to have a FIRM rule that one only gets ride-themed souvenirs if that ride is ridden. The first step is to make sure your budget can handle that, LOL. If not, then figure out the rides you'd really like him to ride, and budget for something from those rides.
So there are no Star Tours or even Star Wars souvenirs if he doesn't ride Star Tours (or Space Mountain if tall enough and important enough, since it's "close" to that theming). No Toy Story related souvenirs if TSMM isn't ridden. etc.
With my guy, the "Mickey-dressed-as" plushes have worked well. He got the Jedi-Mickey plush after Star Tours. He got the Indiana Jones-Mickey themed plush after he was tall and brave enough for Indiana Jones. etc.
Of course, this is a rule I keep for myself, too. DH is a little more liberal, but DS and I *have to* go on a ride before getting a souvenir from it.
SInce it's a more family-wide rule it's not a rule that gets questioned at all.
Too bad I didn't know this when my son was younger! We took him to WDW when he was to be 5, and he HATED the fireworks or anything loud. Didn't have the earplugs, so we had to hid and I wasn't able to watch either Wishes or Illuminations, I was so bumped! 
