Your thread is getting me in the mood for a return to Universal! It's also interesting to me because it sounds like my first trip to Universal. My kids were about 14 and 10 and I went for Harry Potter (I'm a huge fan). Kids knew very little about Harry Potter at the time, but left as huge fans. My older daughter is now grown and works at Star Wars Galaxy's Edge at WDW. She's also a Universal AP holder and goes to Universal quite a bit - for Harry Potter!
On our first trip, I did the same thing as you. Stayed at Hard Rock (2 nights), early entry to HP, Express Passes. I totally "winged it", knowing little about Universal. I did have lanyards for each family member, with clear ticket holders on them. Figured out the rest "on the go". The ride lockers are easy. Don't sweat it. Universal is super easy compared to Disney, IMO. (Disclaimer - that is my own personal opinion, and I appreciate that others might feel differently).
On that first trip, both kids loved going to Ollivanders and doing the interactive wands. It was the highlight of the trip for them. They still have their original wands. (HP geek alert - Vera Bradley has a Harry Potter line where the backpacks, slings, tote bags all have wand pockets!). Spell casting is fun and is a big part of the HP experience for younger kids. Heck, my kids still bring their wands. As others have suggested - since Ollivanders is available as part of early entry, I'd do that and use your Express Pass for the rides. HP is super immersive as I'm sure you know. Just walking around Hogsmeade and Diagon Alley is fun. Grab a Butterbeer and cast some spells! Your kids are the perfect age for that.
Regarding Hippogriff... it's more of a "kids" rollercoaster. A similar coaster at Magic Kingdom would probably be 7 Dwarfs Mine Train. Hippogriff is not as intense as Big Thunder Mountain Railroad at MK, which is nothing compared to the "super coasters" at Universal. Hippogriff has a super cool view of Hogwarts as you go up the hill. It's worth riding for that alone.
I also agree with previous suggestions to get a late breakfast at Three Broomsticks or Leaky Cauldron. Food is good, environment is stellar. I'm sure your kids will also enjoy riding Forbidden Journey, Gringott's, Hogwarts Express. I have not ridden Hagrid, so I cannot speak to that. For my family, Harry Potter is much less about "rides" and more about just hanging out in the Wizarding World.
Note - outside of Harry Potter and the Jurassic Park areas, I could care less about Universal. I am prone to motion sickness and don't ride many rides there. My husband enjoys Universal. He's he's a big thrill ride rider, does not get sick on screen-based rides, likes super heroes, etc. On that first trip I recall that my kids also enjoyed Transformers, Mummy, Jurassic Park River Adventure, Spider Man, and Hulk (although one of my kids admitted to being super scared on Hulk). On a later trip they also liked the King Kong ride. We always end the night in Diagon Alley, which is super cool lit up at night with the Gringott's dragon blowing fire.
Have a great trip!