Gatsby's personal journey was one that brought him from relative poverty (we can stress the term relative,I think) to great wealth. No one in the story came from a more humble background than Gatsby and no one reached as high into areas of influence and wealth as Gatsby did.
This achievement was his dream and his struggle and may also be considered his largest, self-inflicted illusion. Wealth did not transform him into a powerful person. In the end, Gatsby was still unable to win the love of Daisy.
The Great Gatsby is about Jazz Age values, so the theme of wealth and poverty is very important to the novel. Characters like Tom, Daisy, and Jay try to fill their emptiness with material possessions. Nick comes to realize that idea of the American dream has been twisted by people like the Buchanans, who use others for their own gain. Instead of being a land of individuals, America has become tainted with the same ideas of privilege and heredity from which the settlers fled. Pay close attention to Nick's reflections at the end of the novel--these reflections are key to your theme.
The theme of wealth and poverty is directly tied to the theme of illusion versus reality. A character like Myrtle is trapped in her world of poverty, yet she feels like she transcends these boundaries by sleeping with Tom. She berates George and tells her friend that George isn't fit to lick her shoe, yet he is faithful to her and provides what he can for her. But she is trapped in her illusory world and believes that she is better off having an affair with Tom.
Indeed, the Jazz Age was one of moral decadence with greed, materialism, and amoralism as integral parts of the era. With the onset of the automobile, the possession of material goods became the vehicle for social advancement in the shallow realm, at least. It meant being able to purchase beautiful shirts, gorgeous cars, resplendent houses; however, it did not allow one into the inner sanctum of the socially elite. Gatsby is forever West Egg; Myrtle Wilson dies in the Valley of Ashes although she could bed Tom Buchanan of the socially elite. Money buys material possessions, but not social position and not friends.
I think that you can obtain some broad strokes for an essay that you compose via participation in this forum. In terms of the topic, I think that wealth and poverty play a very large role in the story. Simply put, no one in the novel wants to be poor. Everyone seems to be enticed by the world of wealth and privilege, of social ascension where the "flappers" dominated along with material prosperity. Most everyone in the novel associates wealth with value and there is little to indicate that there is nobility in living modestly and within one's means. Rather, the extravagance and opulent nature of the Buchannans' lifestyle and Gatsby's parties seem to present a view of wealth where more is good and where greed for money is seen as an advantage, as representative of "those things that are best." Poverty, in contrast, is reserved for the George Wilsons of the world, and seen as the result for those who have little else to show their worth as human beings. The vision of wealth presented helps to provide the primary motivation for many of the characters in the novel.