woohoo, we are also primarily Disney folks, but we LOVE Universal. Last trip there was last Thanksgiving, and it was BUSY. I would expect spring break to be busy too, so factor that into planning. If you're used to crowds at Disney, bring that crowd- planning mentality over to Universal, at least when it comes to meals, rope drop, etc, although express pass will help tremendously with crowds.
HOWEVER. Universal is so much more laid back, no FP planning at 60 days, no ADRs at 180 days, etc, so that's nice
Just don't try to eat at the popular times, gets very busy esp in the evening,
Even with express, we did have some waits. One time Rip Ride Rocket was 30 mins, Fast/Furious took us over 30 mins, etc. but that can also happen at Disney when lines back up, rides down, etc. but most moved very quickly w express. I think you miss a lot of the regular queue at FJ tho, so might want to walk that whole queue, maybe in the AM. I dont' think you miss anything at Gringotts w Express.
As far as food, QS in U/IoA is awful. BAD! Just think the worst QS in Disney (electric umbrella) all over the place. we actually opted to leave the parks and eat on City walk. We enjoyed Toothsomes, the Bread Box, and Cowfish (and Burger King for the pickier eater...) but I do second the PP's recommendation of the Irish pub. It was good. I have read/heard really great things about NBC café, so that may be a good option. But there are places for burgers/pizza throughout, The place in Jurassic park area was tolerable for that kind of food. NBC on City walk was ok. Craig and Ryno have done several vlogs/reviews of City walk and Universal restaurants, so check those out
We loved Florian Fortescue's for ice cream in DA. YUM! plus butter beer. Oh , the HP restaurants are fun, and to me a must do if you have HP fans. Food was just so-so though.
The horror makeup show should be fun for them, Are the kids HP fans??? In Diagon Alley, there's a brief Deathly Hallows show, and in Hogsmeade, the Frog Choir ( a little dull for my son) and Beaux Baton/Durmstrang show were good. Def do whatever projection show they're doing on Hogwarts castle. They are great! We skipped the nighttime show while were ther,e only because we ended up lingering in the pool at Hard Rock too long. Great pool. If your sons still kinda do character meets, there's Scooby doo and the gang, in Super Hero Island (Spider man, Capt America, etc), the Simpsons. My son loved the Simpsons area, and started watching the show after our trip. Kids didn't know who the Blues brothers are, but they still enjoyed watching them for awhile
Have fun!!!!