I was also thinking that maybe we do an evening FP on the day that we go to AK as I'm sure we will only stay part of the day and then do pool time. Is that a better plan?
Would you have FP+ for AK on that day? In which case you would not be able to get FP+ at Epcot for the same day until you have used all 3 of the AK FP+. By then the Frozen ride will almost certainly have no FP+ available.
We often stay at the Boardwalk and will be there a couple weeks after you. Epcot and DHS are both about a 15 minute walk from the Swan/Dolphin. It is almost always faster to walk than take the boat. although the boat is pleasant when you are hot, tired, and your feet hurt.
It still makes sense to start your day at FW and then wander over to WS when it opens. I would aim for an early-ish FP+ time for Soarin' (the new movie is awesome!) and do the other nearby rides while you wait for the FP+ window to open.
We usually get FP+ for Soarin, Spacship Earth and Mission Space. We were there for a last minute trip over Christmas and there were no FP+ for Frozen, so we didn't ride it. We did Test Track in the single ride line, but my kids are older.
Beth, mom to older DD (8/01) and younger DD (10/06) and always missing Leah (4/22 - 5/1/05)