Don't sweat it. Universal is a whole other world compared to Disney when it comes to schedule and dining.
We went to Disney this past November, and like you we had it booked a year in advance, bought all the guides, made our touring plan, booked ADRs the first morning we could (and had our days and times for ADRs all lined out weeks before that). I don't regret any of it--that level of obsessive planning made it possible for us to fully enjoy our first trip to Disney World.
But then we also went to Universal this past June--we had a Wizarding World package for the week of grand opening, checking out the day before grand opening. The parks were packed. We had no touring plan and didn't make a single dining reservation. And I didn't regret it in the least. It's so much more relaxed--especially since you'll be staying on-site. With an on-site hotel stay you not only get the express pass cutting WAY down on the amount of time you wait in lines, but you also get priority seating at many of the restaurants in the parks and at City Walk. If there is a wait at the restaurant of your choice, just tell them you're staying on-site and they'll give you the next available table (behind other on-site guests ahead of you of course).
The longest wait we had for food the entire trip was about 25 minutes for Jimmy Buffet's Margaritaville (which was WONDERFUL by the way; much better than we expected). Plus, staying on-site, it's a snap to go back to your room for a quick break in the middle of the day without feeling like you're losing out on anything.
It was great to have free dining at Disney, and I'm glad we got to do all of the character dining stuff with the kids for that first trip, but, free or otherwise, without a doubt I'd choose the dining situation at Universal over the dining at Disney any day.
We ate lunch at Mythos in IOA and were blown away with how good it was for a theme park restaurant (they are usually only open until 2 or 3:00 though, so keep it in mind for lunch)--plus the themeing in there is spectacular.
We also ate at:
Nascar Grill--Fabulous burgers, amazing nachos, and excellent service.
Pastamore'--Food was good, and service was okay, but the place was seriously lacking in air conditioning. I don't know if that was normal or not, but the front of the restaurant is open-air straight out into City Walk; even though we sat near the back of the restaurant we couldn't feel any cold air blowing at all. It was hot and HUMID! I wouldn't go back there in summer unless I knew this wasn't normal for them.
Three Broomsticks--We ate there for breakfast as part of our package. The food was just okay (although the Pumpkin Juice was addicting!!), but we still LOVED the place. After all, it is the Three Broomsticks!!!
Honeydukes--For breakfast pastries the second morning. Chocolate Cauldron Cakes and Rock Cakes with Pumpkin Juice--YUM! Just thinking about it makes me want to go back right now.
And there were many more places we would have loved to eat at had we been there longer (Bob Marley's, Bubba Gump Shrimp Co., NBA City, and maybe Hard Rock Cafe just off the top of my head).
Also, don't forget to tell them you're staying on-site when you order at the restaurants--you get a discount! (And if you're not staying on-site, you can still get a discount if you're a
AAA member, so bring your AAA card with you if you have one. These discounts also apply to merchandise in most of the gift shops, even in Wizarding World.)
Don't get me wrong, I LOVE Disney and I can't wait to go there again sometime in the future, but Universal was just so much more our pace. We still had to get up early, since it was grand opening week and our time in Wizarding World was seriously limited, but we got most everything done in IOA we wanted, had time to rest at the hotel, and decided at the last minute what we were in the mood to eat, when we were in the mood to eat it, and still had great food, phenomenal service, great atmosphere and above all a relaxing time together with every meal. It was truly a vacation in every sense of the word, and I want so badly to go back right now!!!
Do a little researching on the restaurants in City Walk to see what interests you, if that's something you enjoy doing (I do!), but otherwise don't worry about it. Just go, play it by ear, and have a blast with your son!