Our most recent trip was our first trip with more than 4 Disney days. Our trip before this had 4 Disney days, but also had SW/IOA/US. Trip before that had 3 Disney days and SW/IOA. And the one before had 2 Disney and SW/IOA. Since you're skipping AK, I think it will be easy. We were always able to get our fill of MK in one full day. (Though it was nice this last trip to have a little more time, but we have younger kids than you making the relaxation needed more!) In the past, we only had one EP day - and that's where we were lacking. Due to that, we stayed in Future World for all three trips and still filled up our day full! It was very much needed to have the extra time for EP this last trip and finally being able to take the kids to the WS side. We had one HS day this last trip, and while it worked, we did run out of time. However, if our crew had been older, I'm sure we could have filled it all in one full day much better.
So, with 4 days and my crew, 1 MK, 2 EP, 1 HS would work just fine. Going every 2-3 years is our plan, so we're not every year people.