I agree with all of the above and have a few things to add...
You should know that there is no Express Passes (EP) for Forbidden Journey, Hogwart's Express, and Gringotts. For the best chance at doing those with short lines, use your Early Park Admission (EPA) that comes with the resort stay.
Speaking of Hogwart's, it's a different experience in each direction, so, if that interests you, plan on riding it at least once in each direction. You need park to park tickets to ride this, so you are covered there.
Since you have park-to-park tickets, if you want to switch parks, you can take Hogwart's or walk. If you walk, as soon as you exit the park, take the path towards Toothsome - rather than walking over the bridge. Walk past Toothsome to the other park. It'll save you some steps and time.
For EPA - make sure everyone takes their room key with them to show. Sometimes they will only check one, sometimes they want to see all of them.
Get some lanyards with the plastic, zip-type pouches. To save some money, get them before you go. You'll need to carry at least 3 things with you: room key, park pass, and express pass. The lanyard makes it easy.
Your room key will also get you priority seating at most restaurants. Just ask if they have priority seating for hotel guests and if they do, show your room key.
Don't forget about City Walk for meals, even lunch. We probably eat there for 90% of our meals.
Express Pass is fantastic! The one 'down side' is that you might miss a good queue or a queue that gives you the story of the ride. For example, we rode Mummy a ton of times using Express and loved it, we just didn't quite understand what was going on with the story. One walk through the main queue and we got it. Some other queues that might be worth it if the line is short - Men In Black, Kong, and ET (we've never done it, but have heard some say it's their favorite). If waits are long, don't worry about it, you'll still enjoy the rides.
Do NOT mistake Rip Ride Rocket for a ride with an interesting, or otherwise important, queue!
The walk from Royal Pacific to City Walk is a nice walk. We don't do it often, since there will be plenty of walking in the parks, but it is a nice, quiet, change of pace.
The boat service is so easy. We do EPA, eat lunch in City Walk, then head back to the hotel for a mid-day nap. Then we go back to the parks for a few hours before dinner.
As
@gotomu212 said, that's also a great way to plan the water rides. Hit them all in a row (they are all in the same area of IOA), then head back to the hotel to change.
One difference from Disney - a lot of the rides at Universal do not allow you to carry on items. For some (Hulk, Dragon Challenge, and Rip Ride Rocket), you have to completely empty your pockets. Free lockers are provided near the rides.
The exception to the 'free locker' rule is the water rides. They do not make you store your stuff, but if you choose to, those lockers have a fee.
Last thing you should know - staying on-property at Universal will completely spoil you! Simple transportation to the parks, early entry, and - the piece de resistance - Express Pass are simply amazing! We can't go back to Universal and NOT stay on-site.
I have to agree with previous posts it is so much more relaxing than Disney. The Express Pass that you are going to get with staying at the Royal Pacific is great. Once you get those it is hard to tour a park without them. I went to Cedar Point twice last year (favorite amusement park) but to get their fast lane express is very costly. Here the express pass is right in your room rate so you don't think about it. The hotels are really worth the price. Universal does a great job with them.
