In the opening pages of the story, what details of setting, of characterization, and of dialogue foreshadow later events?

A good question.

Consider the first statement about the daughter: " The daughter could not see far in front of her and continued to play with her fingers."

She can't see far ahead literally—but she can't see what's coming either.

When discussing Mr. Shiftlet, O'Connor gives us this line: "He held the pose for almost fifty seconds…" He is a poseur—one who poses, or takes on certain positions. He means to deceive. He then drops the pose, as he does in the larger story.

Of course, my favorite line is Shiftlet's: "Nothing is like it used to be, lady," he said. "The world is almost rotten."

Nothing is like it used to be—the mother used to be young, have hope, etc.—but the key point is that he tells us the world is rotten. He's rotten, and will do lousy things.