Even though I am not a Park Hopper, it is definitely not useless. In fact only having a 4 day pass, it is probably a necessity for you. I know for our family, we do at least 6 days and it isn't enough time.
It seems that taking a day out for Universal, you will be very rushed at WDW and it would be better to not be locked into one park per day.
The biggest advice is to get a Disney guide book. "The Unofficial Guide to Walt Disney World" is one of the best. It also gives you access to Touringplans.com for crowd calendars and the best/worst days to visit parks.
Also, staying on-site means you can take advantage of Extra Magic Hours which give you even longer in the parks. So for instance, on April 27th, Epcot has night time EMH from 9pm until Midnight. Only resort guests can ride attractions during that time and it is open later to give you more time. You can start your day at Animal Kingdom and then when it closes at 6pm or earlier if you wanted to, hop to Epcot until Midnight.
I looked and MK only has Morning EMH during your stay. Epcot offers AM and PM. DHS has AM and PM. AK offers AM only. So use these to your advantage to get more time and more attractions in.
The rest of what you asked is totally subjective to the person posting it. There are many who think Animal Kingdom is a half day park. I totally disagree and feel it is easily a full day park and would like it to be open later. You can "run" through it in half of a day, but you miss out on a lot. At AK, the "musts" for us are Festival of the Lion King, Finding Nemo the Musical, Killimanjaro Safaris, Expedition Everest. We have to eat at the Flame Tree BBQ at least once. AK has my favorite Parade, so we always have to see Mickeys Jammin' Jungle Parade. And this being your first time, I wouldn't suggest just running through any park. Take your time and take it all in.
At DHS, I actually consider that one a half day park, but that's because I'm not a big fan of Fantasmic!. But being your first time, you should see it and judge for yourself. You will need to line up at least an hour early to make sure you get in and get a good seat. Other musts are Tower of Terror, Rock n Rollercoaster, Star Tours & Toy Story Midway Mania. For Toy Story, it is best to get there at rope drop and grab a Fastpass right away. They will most likely be gone by noon, especially during spring break.
Epcot, This is tough for me because we always do 2 days because we love it there so much. You should definitely do Soarin', which like Toy Story Mania, will need a FastPass right at rope drop or you will be waiting at least an hour in line...often more. Test Track and Mission Space should also be done. If you like Finding Nemo, then you need to go to the Seas pavilion and do Turtle Talk with Crush and the Nemo ride. That's already a lot and we haven't even made it to World Showcase. Make sure to do the boat rides in Mexico and Norway. Watch Myuki make candy in Japan. Eat a pastry in France and much more I'm forgetting.
Then to MK. Not sure if you are a coaster person, but you should do all 3 "mountains". Get a hot dog at Casey's Corner, Buzz Lightyear Space Ranger Spin, Carousel of Progress(it's a classic), It's a Small World(Classic), Pirates of the Carribean, have a Dole Whip Float in Adventureland. I know you'll get a lot of responses to your thread, so I'll just stop there.
Have a magical trip
