Regarding Littlefinger's fate, there is one factor he has not considered:
Robin. The sole reason Littlefinger is Lord of the Vale is that he married and then killed Caitlin's sister, and is now the foster father of Robin.
But if Robin were to marry someone...say, a lady of Winterfell he is fond of and who he sees as his motherly substitute...then Littlefinger loses all power and claim to the Vale, and becomes expendable.
Littlefinger having command of the Vale's forces and Lords (who all fucking hate him) is the reason the Stark's havent turned on him.
Sansa has the need for getting rid of him, Arya has the means.
As for the meeting of all forces and the finale, I think that yes, the Wall will either crack or fall this weekend as a Cliffhanger, signaling that Winter is coming to all of Westeros, and thus the White Walkers can finally attack en masse.
The meeting will definitely have Cersei either plotting something or betraying them outright.
My money is on either Trial by Combat (Cleganebowl!) or Jamie finally snapping and getting his Queenslayer achievement/trophy. (he's already got the Queenlayer one, but thats a minor one)