Use the permanent's mana value as it existed on the battlefield to determine whether you scry.

If the target permanent is an illegal target by the time Perilous Voyage resolves, the entire spell doesn't resolve. You won't scry.

If a permanent has {X} in its mana cost, X is considered to be 0.

There are many important moments in the story, but the most crucial—called "story spotlights"—are shown on cards. These cards have the Planeswalker symbol in their text box; this symbol has no effect on gameplay. You can read more about these events in the official Magic fiction at http://www.mtgstory.com.