I used
UT for both my Universal and Disney World tickets since they were cheaper. There's not much to tell or I can remember about UT at Universal. I know I printed them out but don't think I needed to change them into tickets at guest services but someone else can respond to that. I do know that before using our last day of a three day ticket I did go to guest services and upgraded all our tickets to seasonal passes. Each upgrade cost me about $15 and we used the tickets when we returned this year.
There is way less planning needed for universal but you should read ride and show descriptions prior to going to make sure you hit the shows and rides that interest you and that the group can stomach. I say that because many of the rides are roller coasters or simulator rides that can really do a job on those with motion sick issues. That's my problem but had great success wearing a prescription patch for all 3 days.
Also, since there are two parks next to one another you just want an overview so you have an idea where things are located.
Of course, the Harry Potter areas are a must see and although you need a seperate ticket (park to park) to ride the potter train it is fun to do once. Ride both ways because the scenes are different and you want to get your monies worth. I bought my daughter the wand but she became frustrated because most of the interactive sites didn't really work and lines were long. We didn't even bring the wand this trip but I was watching those with wands and most had no luck with the interactive sites. Surprisingly, not many people in this site mention this issue. So, if you need a wand I would recommend just buying one and sharing.
Not sure how much the 5 year old will be able to do at Universal or how much would interest him/her. I didn't bother with Universal until my kids were tweens.
Also, we make a dining reservation for a sit down lunch at Mythos about 30 days prior to our trip when ressies first open up. There aren't many full service places inside Universal or islands of adventure because most are in city walk (and many city walk places don't take ressies) but I don't like having to do all that walking and waiting for a table just to eat. So you may think about that if you don't want quick serve.
Like Disney you will see people dressed in Universal/Potter garb.
Enjoy your trip.
