I think you could classify people according to wealth because it seems to be such a big theme in the book.
1. THE BORN RICH: Although Tom and Daisy are filthy rich, it feels like they don't deserve it because they didn't work for it. It is as if now they live off the interest of someone else's work in the past. Often we call this old money. This was certainly noted because they lived in East Egg.
2. THE NEWLY or ILLEGALLY RICH: Gatsby fits in this category with many of his associates like Wolfsheim. These are those who scam others and disobey the law or take advantage of the current situation to get what they want... no matter the cost, even if it means their very own souls.
3. THE WANT TO BE RICH: Even though we like Nick for his down-to-earth character, he certainly had hoped to join the group of Easterners who were wealthy. I think it is why he went into stocks and bonds. Jordan Baker fits into this group as she ran in the circles socially with the rich but we never see what she really earns. Even old Mr. Gatz seems taken with the idea of wealth, yet he would never know how to acquire it himself.