More thoughts: there are probably ride videos on youtube, so you can watch and note when any scary things (in your son's opinion) might show up. With us, DS really doesn't want to see the acromantulas. So we've worked out when he closes his eyes for the spiders (I think the cue is when the dragon breathes fire?) and then I squeeze his knee to let him know when they are gone. The audio cue for that, I think, is when you hear Hermione, but I have weird hearing so I have to keep my eyes open b/c I can't always hear her.
We found there to be plenty for a boy of that age to do. My son who had his first Uni trip at 6.5 and is now 9, enjoys Uni FAR more than he does WDW. With our family Universal Orlando is right up there with
Disneyland, and WDW is below them.
The Marvel characters are very fun when they ride up on their ATVs, and they are very personable and good at their characters. Spiderman requires a line to meet him, but he's inside. Consider budgeting to buy the picture with him (otherwise your picture of them will be just a green screen behind them...I've been working on a trip report from Feb and the link is in my signature, and you can see the difference between green screen and purchased pictures there), or even look up the Photo Connect info on this board for more photos!
And lastly, I'm going to strongly suggest you go through the Curious George sprayground (I think that's what it's called), following the footsteps on the ground to keep yourselves dry, and find the ball play area. It's indoors, which means it can get warm (though there are fans). There are tons of soft balls, and then things to suck them up, things to shoot them out of, there are two levels of play area, and it's a HUGE amount of fun. The balls are so soft that I've seen a toddler get beaned in the face with one, and she didn't react at all. They are soft.
I might have a proper park map hanging around that I could mail you; I'll look for one later today, and if you would like me to mail one (if I find one) send me a PM with your address. It's way more fun to plan with a proper map, IMO. (though it won't include any of the new Simpsons stuff)