Your plan is totally do-able. Just like WDW, some attractions have longer waits, while others tend to have very short waits. Universal also has several shows, and most of the shows have ample seating, IME. When it comes to show, s arriving a little early = a better view, but mostly when we've gone to shows at Universal they have LOTS of seats.
I'll also say that all the big parks are special after dark, but the Harry Potter areas get a special bonus after dark. An option you might enjoy is just to spend that first evening in the HP areas, especially if you will be hopping. In my experience, evening is good time to go on the HP rides. Even if you don't go on rides, you'll probably enjoy walking around the HP areas as there is much to see.
If so, an option you might want to add is to get the wands. They run about $50 each, but the spells are great fun! You start by going to the Olivander's show. If someone in your family gets picked- voila! If not, you can pick your own wand. Then you can walk around doing the spells, all over both HP lands. The spells sometimes get short lines but only ever a few people deep. If there's nobody in line, then you get to use the map to find the locations yourself. If others are in line, then you get to see HOW to do each spell. So both can be good.
Even if you don't buy wands, I think it is fun to watch other folks do the spells. The HP areas also have unique foods and beverages, so they are fun spots just for snacking, too.
In general, touring Universal is less stressful than touring MK in that you aren't bound by strict FP time windows. You don't need a strict touring plan. There' only a few key things to know - the rides near the very front of the park get crowded at night. Expect long lines for Minions and Rip Rocket.
If it is WARM, you could also use that first night to do the WATER rides. Expect to get drenched. Wear a swimsuit, shoes that can get very wet (??Keens?
Crocs? something along those lines), and try to avoid bringing any kind of bag.
Oh, that's always true at Universal. On many rides backpacks have to go in (free while you ride) lockers. If you are only in the parks for a few hours, then you'll do well to go without any kind of bag, because it is much faster. You'll be able to go directly on/off the rides.
Unless, as I said earlier- you get wands. Wands also have to go in the lockers before you can go on most big rides. So that's another reason to spend the first night doing just HP and wand spells. (Then on your full day- leave the wands in the room- then on day 3 bring the wands again with you to see the spells during the day.)
A few rides - Hulk- you can't have ANYTHING metal in your pockets - so you pretty much have to have someone hold your stuff, or put your stuff in a locker. The Lockers are FREE while you ride, so long as you return within the permitted amount of time (about an hour). It just takes time to use them and retrieve your stuff.
We don't use a complicated touring style at US- even when we don't have EP. Our strategy is usually just to skip any line that is more than 30minutes, and just return later. It is often a good strategy, if you don't mind a little walking.
The one ride you'll want to do VERY early on at least ONE of your early mornings is Minions, as it pretty much always has a long line.
