Wow first off have fun.
That said, I would recommend taking breaks in the afternoon. Going for that many days will bring on exhaustion fast. Even the best of athletes need rest at WDW...lol
Know you will not see all of anything, make a list of some must sees your first time and take your time. People who have been every year for years, still report not seeing it all. So don't go to fast and miss what you are seeing.
In MK, I recommend Carousal of Progress. It was built by Walt for the World's fair way back when, way ahead of it's time. Of course now it is not so, but as you sit and watch it, remember this was in the 40's or 60's (can't remember which), so it was "cutting edge".
If you love Walt, it will inspire you.
Next I would recommend eating at Crystal Palace in MK. Hopefully you have an adr or try and get one before. It is so cool, reminds me of Mary Poppin's time and has really good food.
Another thing is to always be aware of what you are smelling. WDW pipes in fragrances to enhance people's experiences. It is wonderful how this little bit of info or "thing" really makes you think....hmmm, customer service. lol
For your feet I would recommend running shoes, broken in and a new pair of
crocs that are not. Alternate them and if you can wear the shoes in the morning and the crocs at night. This will really help your feet. As your feet swell during the day the crocs "make room" for that.
While in MK, look for "PUSH" the talking trash can. He is usually somewhere in tomorrowland. Truly a wonderful little thing to watch. Again WDW goes above and beyond with this feature. Try and find the guy in the crowd controling him....it is fun.
Most of all have fun, relax and enjoy your trip.
