Hey, thats the flight hubby and I took last Sept.
And just go ahead and schedule a nap that day. Boy was I tired.
Also, sleep on the plane. Don't let that in-flight movie distract you, just close your eyes and sleep.
We made PS Ressies at Boma (AKL) for breakfast. It was great. We arrived a little earlier than our ressie but were seated quickly. The great breakfast provided a burst of energy for our morning. We went into the AK after breakfast. But only lasted a few hours. Then took off in search of forgotten supplies/extra sunscreen.
After we got into our room, which was ready several hours early, we napped. Then hit MGM for an hour or so that evening.
Based on how tired I was and how many naps I took the couple of days after the flight I don't think you should plan on serious park time that day. Do a breakfast at one of the resorts. You can always play some mini-golf, do downtown Disney, get your grocery shopping done. Maybe return to a park in the evening.
We wish it didn't take all day (or night) to get to WDW from Seattle. We are glad Alaska is starting there non-stop service to MCO this week. That should cut off a couple of hours.