Let's begin this question with who has money: Of the characters in your list, Tom, Gatsby, Daisy, & Jordan have money. The others don't (or not enough to compare). Next, it's important to remember the difference between new money and old money. Gatsby is new money, and that's one reason he's looked down on by Tom. Tom, Daisy, & Jordan are all old money-- their families have been wealthy for generations and they don't flaunt their wealth with a lot of flashy possessions. Of those who don't have money, consider their contentment-- who is happy with what he or she has and who wants more?
Next, consider the characters who change in the story. How does money (having or not having, wanting or not wanting) make them change? Nick doesn't have a lot of money (althogh his family does), and he doesn't really want more-- he's more or less content with his life. So how does his encounter with the wealth of Gatsby change him? How does seeing the poverty of the Wilsons change him? Does he see things differently after these encounters?
Gatsby has made a pretty big change in his life-- he went from dirt poor to filthy rich. Obviously money was involved, but did his personality change? What did money give him the opportunity to do that he really wanted?
I hope this gets you on the right track. Good luck!