I had to edit down the original question.  I invite you to repost the second half of the original question in a separate question.  I think that nihilism can be seen in Macbeth in a couple of settings.  The entire element of Macbeth seeking to usurp an established order in the desire to take the crown could, in of itself, be seen as nhilism.  The rejection of the established moral and political order are nihilistic elements that are present in the drama.  In terms of the characterizations present, when Lady Macbeth speaks that she can "unsex" herself it is a rejection the traditional conception of gender.  Macbeth's soliloquy in Act V is nihilistic in that it rejects nearly everything of value and meaning.  The idea that consciousness is "full of sound and fury, yet signifying nothing" is reflective of a nihilistic order where there is no conception of justice or any sort of moral order that drives being.  Macbeth's dawning of understanding that emerges in the final act of the drama is one in which nihilism is shown to be intrinsic to being in the world.