My DD tends to be rather timid, but she isn't about WDW.
When she was just under 3 years old her best friend came with us (his family) he tends to be very scared of things, but for the most part did fine because his best friend was there and she was really comfortable.
Prepareing is a good thing. The sing along song viedos with the them parks is great (The
Disneyland fun one too, it is close enough to MK). It also gets them ready for how the charaters will look (how big they are.) They help prepare him. Look at maps and other planning things. I agree a glow or light up toy is great. We like buying a spinner there because it keeps them busy. We did make the mistake of leting my friends son chose what he wanted to go on 1st (buzz) and it scared the pants of him. He was able to clam down (after getting a new buzz light spinner.) and we chose the next rides (dumbo, carosel, peter pan,) worked our way back up. He was fine, infact sometimes he is more brave then my DD.
I wouldn't push any rides unless he is fearful of all of them. Start slow, be sure if you tell him it isn't scary, it isn't. I remember being in line for dinoaur and this parent was yelling at his young kid ( 7 or 8 years old) that dinosaur wasn't scary and to just get over it. HELLO, that ride can be terrifying!

If you say it isn't, and it is he won't trust you again. There are lots of non ride atractions to start out on too. Maybe don't do many rides the 1st day. Ease in as much as you can. Also the face charaters are much less scary for kids then the costumes.
TTA can be good to start of, just be ready for the dark. Really just be ready for everthing so you can prepare him. When you are there prepare him buy maybe letting him see one of you ride a ride or interact with a charater 1st, to see that you are fine. DD didn't want to see the charaters for a while, but she wanted the picture and autograph, so she would go up there and get it, but not want anything to do with them. She is much better now.
Dont' have a lot of expectations of getting everything done. That isn't going to happen. But have fun doing what you kid wants to.