F2, in his political will, expicitely called the imperial diginity a "hollow title" and "without substance", since J took his power form the Habsburg domains, not the imperial position.
He was ambitious, but on a lower, more concrete level:
He mentions the upcoming inheritance of Ansbach and Bayreuth in Franconia, with the possible option to acquire Nuremberg.
Also, he puts some hope in the possible extinction of the Dukes of Mecklenburg, in this case Brandenburg has a strong claim. As the Electorate of Hanover also claims the right of succession, F2 expilitely tells his successor that he must be willing to enter Mecklenburg by force (when the last prince of M dies) and expel Hanoverian troops that are also there.
Furthermore, he advises his successor to use every possibility to annex Saxony, since that not only is a rich country, but would also help to protect berlin from Austrian attacks once the mountain passes, Torgau and Wittenberg are fortified and garrisoned.
[To achieve this, he suggests waiting for a time when Russia and Austria are both entangled in a war against the Ottomans; and the King of England (his words!) either disinterested in German affairs or occupied by a war against France. Then the Prussian army should invade Moravia and send help to Hungarian insurgents. After a Prussian victory in Moravia, Austria would get that province back, but would be forced to cede Bohemia to the Wettin Elector as compensation for Saxony.]
[[To acquire Saxony, he also regards giving away the Rhenish possessions in a multiple-partner deal as acceptable price.]]
If possible, West Prussia with Danzig and the Ermland should be acquired as well, since without it, East Prussia is indefensible against even a weak Russian advance. By owning Danzig, Prussia also controls the Polish grain exports and can thus maintian a stranglehold over the economy of a revanchist Wettin-ruled Poland-Bohemia.
Swedish-Pomerania would be highly beneficial as well, but should be only acquired by treaty.
Generally, F2 is big on territorial consolidation of the domains to gain a well defensible state. This includes giving up indefensible exclaves if a better position can be gained. He specifically mentions the idea that his successor might apply pressure to the dukes of Mecklenburg-Strelitz and -Schwerin to move to Ansbach and Bayreuth to give up their ancestral lands and take over the Franconian domains.