This is what we're doing. Sunday (arrival day), Monday and Tuesday, no EP. We plan to scope out the park, hop on rides with low-sh wait times, see a show or two, play with the interactive windows, eat some treats, etc. We're also staying at Cabana Bay, so the lazy river might be calling my name in the afternoons. Then we'll have EP on Wednesday and Thursday, and we'll use those days for riding and re-riding our favorites. I don't know if we'll really NEED them, but having EP is the best way to improve our MIB scores.
Last time we went, we started with EP, and after two days we felt like we'd really "done everything" we wanted to in the parks. The second two days of our trip were really laid back, as we repeated some of those things and took in shows, etc. My opinion is that 2 days with EP or 4 days without EP is sufficient to do most things during most of the year.
Also remember that spring break has not only larger crowds, but longer hours. Including EPA, you will have 15 hours a day in the parks. If you go at a less busy time, you would only have 10 or 11. Take advantage of EPA, monitor the virtual line situation (have multiple people in your party trying to grab a place from different phones), and watch the wait times on the app so you can jump on rides with lower waits. Take a break in the middle of the day when the park is most crowded, and go back in the evening when it starts to empty out. Use the non-EP days to watch the entertainment and do character meets. Right now it's 9pm for a 10pm closing, and I just checked the app for ride times. Hagrid's is virtual line, Gringotts is 90 minutes, and everything else is 25 minutes or less. That's a Sunday night during spring break. Not too bad, if you're willing to stay late in the park.