I believe it is important to first think about what you and your family(?) will enjoy doing, given personal preferences, ages, physical conditions, etc.
For example, we went last May: DH (me), DW, DD14, DD12, DD8 and stayed at the Poly.
We knew from a couple of visits to Wonderland that 7 or 8 hours per day on the rides was enough for us. We were not interesting in any "commando" days at the parks.
Now, we all really enjoy eating, so we were on the dining plan. Every day ended with a table service meal around 7:00 to 7:30 at night, followed by fireworks viewing (sometimes from our balcony), then a swim. We found this very relaxing, and none of us suffered from tired feet or anything else while we were there.
We did not have much of a plan for visiting the parks. Before we left, we did make a tentative plan on which parks to visit on each day, which was partly driven by our dinner reservations, and partly to space things out (for example, no water parks on adjacent days).
When visiting the parks, we had some ideas in mind about the must-sees, and if they were likely to be busy. (All of this info gleaned from these forums!) So when visiting Epcot, we went to Soaring straight away to get a fast pass, but that was one of the few times. For the most part, we had no "attack plans", we just walked around the parks and made good use of the Fastpasses as we went.
Early May is neither busy nor quiet time. If it had been a busier time, this may not have worked so well. So if you go in a busy time you might need to plan more.