Write this response in 3 pages: No one knows very much about Gatsby - he is quite a mystery. What are some of the things we learn about him in chapter IV? Can we be sure these things are true? Does it matter if they are? What do we learn about Gatsby's past with Daisy? How has everything he has done been part of the plan that finally comes true in chapter V?

If you have only three pages and you want to offer some critical investigation, you will want to be efficient in your answer. I'd start and end with an overarching paragraph that synthesizes the various things Nick learns about Gatsby in this chapter, clustering together the various elements of gossip or deduction that are offered.
We begin with rumors about Gatsby's criminality—bootlegging and murder—and these seem to be supported by the catalog of guests who attend his party and later information we learn. While some of these things that others say about Gatsby are largely untrue, Gatsby's business dealings with Wolfsheim are clearly true, casting credibility on the bootlegging rumors at least.
Gatsby then offers his own story, which is a mixture of truth (Montenegro) and fiction (childhood). It is clear that he makes up many details, and it is curious that a man from northern Minnesota would tell a man from St. Paul that he was from the Midwest and then name San Francisco. Nick, like the reader, vacillates between the things that seem true (e.g., he is able to avoid the police ticket with a card from the commissioner) and what seems patently false.
Jordan corroborates some of the information that we will take for granted regarding Daisy and Gatsby's past. While she is not particularly honest herself, we have no reason to doubt this story, even if it is crafted to convince Nick to hold the tea party. From Jordan, we learn about Gatsby's hopelessly romantic quest to capture the past.
The mixture of fact and fantasy in all of these stories makes Nick want to believe in Gatsby, and that same aura of enchantedness tends to draw the reader in as well. Faced with the alternative of the tawdriness of all other ways of being in the world, Gatsby's invented identity is vastly more appealing to Nick, in its romanticism and its earnestness. If being the invented version of himself is necessary to achieve the authentic desire Gatsby possesses for Daisy, then one can rightly wonder if that desire is more fully his identity than any accident of his past life.
As you write an essay, you might want to organize the pieces of information into categories of true or false, or between debased and elevated, and match up who provides those pieces of information.
The larger question is, does it matter? In different spots in the novel, Fitzgerald sprinkles in little references to Platonic ideals, and in chapter 4, Gatsby says he wants to tell Nick "God's truth." In a Platonic sense, the gods' truth would be the transcendent ideal—not the tangible instances of that ideal we find in this empirical world. If we toggle back and forth between fact and fiction, or between ideal and real, we find they are both true but in different senses. Chapter 5 does seem to confirm, at least temporarily, the enduring and transcendent love Gatsby has nurtured for Daisy. The fact that he invests this ideal love in an all too real and all too flawed and human Daisy is likely the tragedy of the novel.