The movies don't really tell us what Frodo did with Bag End. In the book, he sells it to the Sackville-Bagginses before he leaves with the Ring. Sam and Rosie Cotton move into Bag End after Frodo sails into the West.
Gandalf is telling Aragorn that he must go through the mountain and follow the Paths of the Dead. This is a part of Aragorn accepting his destiny (which he does more readily in the books). The Black Ships are those that you see attacking from the South. Aragorn leads the army of the dead to stop them. I forget how true that is to the book.
Hope that helps.
So even though it was Elrond who told him to use the army of the dead to go to battle, Gandalf was the one had the original idea?
Sorry if this is a lame question.
Quite true, actually. The Corsair ships pull up to Pellenor Field, but then Aragorn's banner unfurls from the mast and reveals that it is actually him his dudes arriving, not the Corsairs.
And then wonder took [Eomer], and a great joy; and he cast his sword up in the sunlight and sang as he caught it. And all eyes followed his gaze, and behold! upon the foremost ship a great standard broke, and the wind displayed it as she turned towards the Harlond. There flowered a White Tree, and that was for Gondor; but Seven Stars were about it, and a high crown above it, the signs of Elendil that no lord had borne for years beyond count. And the stars flamed in the sunlight, for they were wrought of gems by Arwen daughter of Elrond; and the crown was bright in the morning, for it was wrought of mithril and gold.
Thus came Aragorn son of Arathorn, Elessar, Isildur's heir, out of the Paths of the Dead, borne upon a wind from the Sea to the kingdom of Gondor; and the mirth of the Rohirrim was a torrent of laughter and a flashing of swords, and the joy and wonder of the City was a music of trumpets and a ringing of bells. But the hosts of Mordor were seized with bewilderment, and a great wizardry it seemed to them that their own ships should be filled with their foes; and a black dread fell on them, knowing that the tides of fate had turned against them and their doom was at hand.
In the book, though, the Dead Dudes do not accompany Aragorn to Pellenor, they are released from their curse after helping him capture the ships.