Regarding Chapter Three, you can also examine the character of Jordan Baker, an archetype of the new woman of the 1920s, amoral and insincere. She makes the interesting remark that she loves large parties because they are so intimate. What she means is that at large parties there is the opportunity for intimacy because few people know her and because she can slip off with someone more easily even though her dishonesty in a golf tournament haunts her.
You may also like to examine Owl Eyes, who is observant enough to notice that Gatsby's books have printed pages. And, yet, he becomes involved in an accident and the "violent confusion of the scene." Nevertheless, he says things indicative of "washing his hands of the whole matter," such as "I know very little about driving--next to nothing" and explains that he was not driving.
Regarding Chapter Four, much of Gatsby's past is revealed. Gatsby's illusions are tied to his belief in material values as the "fairy's wing" of his dreams of attaining Daisy. You can explain how.
For chapter 3, you could write about Gatsby and use his parties as a symbol for him as they represent the importance of appearance over authenticity. Gatsby's library also comes up in this chapter and though all the books are real they are also unread.