I just don't understand how this battle is supposed to go down. Army of the dead come in and overwhelm the living army. They don't have enough fire power. They'll have to lose living troops in masses vs the dead hordes. Even if the army of the living defeat a large portion of the dead, it will be logically impossible. As we saw beyond the wall, the dead rise again after battle, and in even greater numbers due to living casualties. The Dragon's aren't safe to burn the dead army either.
It just seems like a losing battle overall. Not sure how they're going to twist it all around, but the army of the dead should realistically, almost kill every single person easily.
The Nk's army will split up, with a portion going to attack WF, while the other portion goes towards KL. I think the WF battle will be episode 2 or/and part of 3. Many will be lost, WF all but destroyed, but the living will prevail. The WF army will be greatly assisted by the vale, Dany's forces, and a rag tag army quickly thrown together/recruited by Jamie/Bronn (left over riverun forces, maybe some Freys/mountain people/ maybe even some crannogmen?). Meanwhile the other portion of the NK's army, and the NK himself march to WF, and that battle will be in episode 5. So perhaps the WF battle will never see the NK and his dragon (all though it is possible he could make an appearance in it as well), but will not have at his disposal all the wights (hey it takes time for an army of wights to march to KL). This leaves episodes 3-4 with Cersie/golden company/Euron vs Theon plot. Episode 6 to deal with the aftermath.
Not wrapping that in spoilers because all based on speculation vs the things I have heard.
Also, didn't a good portion of the Keeps forces under Randyl Tarley take a knee to Dany after the crushing defeat on the supply line raid? I have not heard them mentioned.
Maybe Theon, after defeating Euron and saving Yara, returns just in time with (maybe) some Dorne/Iron island fighters to assist in the KL's battle, that would help to complete his redemption arc (before he dies).
If Jaquen does make an appearance in season 8, the most likely spot would be by infiltrating the Golden Company army killing the commander and assuming his identity. this is turn would add another large force to help against the WW's at KL.