To go to war against the Lannisters? Yes.
The LF on the throne thing woul dhappen later.
I believe that you said… somewhere… once that the master plan would be for the Young Falcon, Harry Arryn, to win the Iron Throne via right of conquest. Then when everything settles down Littlefinger cuckolds him with Sansa, and once the child of this most creepy of unions is born, Littlefinger has Harry bumped off and Sansa rules as Dowager Queen Regent until “Harrys” son is of age to take the throne himself?
Yeah pretty much.