The burnout is real! I remember it so clearly still even though our last WDW trip was almost 3 yrs ago & on our last day I told my family, “We are most definitely coming back, but I need a 6 month break from looking anything WDW planning related & then we can talk”.
As for on the ground, all our time in WDW was well-spent (even the hour in the Mission:Space playground at the exit because it was A) Hot, B) The most favorite attraction for my little ones at Epcot and C) We were near the end of our trip & it gave me time as the planner to sit with the plans & figure out what do we have left to do that we absolutely didn’t want to miss).
Having all the plans in the world meant we had flexibility to pivot when we needed to & still get all the really top must-do’s done. I cannot stress that enough. Even though there was SO much that I felt I needed more time to do, I didn’t leave with any regrets, at all. Your family will most likely never know what they missed & if it’s important enough to come back to see, you’ll find a way to come back.
As for your plans specifically, I think you’ve very smartly planned in a lot of downtime that I neglected to (partly because I really didn’t understand just how tiring it would be & how little rest we would get following our usual touring style of DLR to hit as much park time as possible).
Your trip is actually the same length as ours was and we also did our park days as HS/AK to begin (but then did MK/EP on 3 & 4) and then did our last 4 exactly as you have HS/AK/EP/MK to build up to a perfect ending. I really liked how that order worked for us & you have it very similar so I think you will love it.
I also love that you have a low-key arrival day & will be doing MK up until you need to head out to the airport. We switched that up & on our arrival day (mostly bc we got to Orlando so early in the morning) we went straight to HS. On our final leaving day, we just had a chill day before going to the airport. We had brunch at 1900 PF & visited both Poly & took the ferry over to MK to get back to our resort as our last thing. You’ll be on that boat ride from MK to Poly to get to the airport so I hope you find it as blissful a goodbye/last look as we did!
Great job & go knock 'em dead (in ~20 days)! And in the meantime, savor the plans you’ve got!