Some thoughts from off the top of my head:
*Naruto's becoming Hokage. High Priority. This is what he has been dreaming of since the manga began, so it's only right that this happens. How does he become Hokage? What kind of Hokage is he?
*Relating to the above. How did Kakashi become Hokage? What kind of Hokage is/was he? How and why did Tsunade stop being Hokage? Did she step down?
*Seeing how one of the plot issues brought about was that the title of "Hokage" struggles to find meaning in a world where peace is prevalent and Shinobi are, apparently, no longer required, what is the shape of the world when Kakashi assumes the position, and then when Naruto takes over? Are they on the path to finding peace or do they still have some way to go before they can broker the proper negotiations between villages?
The way I saw it was that there is still a degree of tension that exists between all of the Kage and their Hidden Villages. Peace isn't a quick fix, so there will be distrust.
Yes these are main priorities that must be included within the ENDING most of everyone in the NS fandom will agree to that no doubt.
The question is how long the ending should be to everything in for a decisive conclusion.
699 and 700 if done right should have ended the current volume of the series as well as conclude the War Arc. If Kishi wasn't so stingy he could have made one more volume worth of chapters to conclude everything left within the story before the end. So for our ending it should be like this:
-recreate 699 and 700 as the last chapters of volume 73 or 74 (can't remember which

)
-then create 10 chapters worth for one final volume to be the Ending of Naruto.
So at least 12 chapters should do for the final ending of Naruto. Within that much we should cover everything the manga didn't conclude or left out from Kishi's ending. X)