Fitzgerald uses the words hope and dream alot because Gatsby is all about hopes and dreams. This is why Nick admires him by the end of the novel. Everything Gatsby does is in an effort to achieve his dream of winning Daisy and he maintains hope in the face of overwhelming evidence against him; Daisy's already married, but Gatsby still hopes she'll choose him.
Nick comes from a well to do family and has experience travelling and being brought up with a solid education. These advantages give him a leg up in the world.
Nick is supposed to be a neutral person which is why all his school friends tell him all their dirt; but Nick immediately shows us that he is biased and will relate the in the story he tells.