Awesome text! I <3 Gatsby so much that I came dressed as the green light for muck up day

...my idea is that I would do a scene after the story, maybe around five years after the end, and it would be about how Gatsby's death was all an elaborate plan in order to make Nick think that he had died, so Gatsby would be able to complete his illegal work with Wolfshiem and not be suspected.
RETCON! Interesting. So are you looking to flesh out Gatsby's more sinister, criminal side? Would he fake his death in a slightly remorseful way at the thought of how upset Nick would be, or is he a cunning mastermind that's engineering this plan to create as much misery and unhappiness as his old life is ruined? And does he still hold a candle for Daisy, since she moves away with Tom after Gatsby's funeral... but if he's alive, is he still pursuing her? Or did the whole running-Myrtle-over put a damper on his affections?
Basically: what are you trying to explore here? I've just given you a bunch of questions that may or may not be relevant since I don't know what the gist of your story will be, but to write an effective creative piece, you really need to consider what the point of it all is. You know how in Text Response essays, you have to answer questions about what the author's message is? Well here, you're doing the reverse, so you have to reverse-engineer a views and values concern.
For instance, Fitzgerald wanted to explore the superficiality of wealth and suggest that money had no value to someone who desired what money couldn't buy, so he had Gatsby attain a whole bunch of money and then made him a tragically miserable character because all he truly wants is his idea of Daisy (interesting side note: is he in love with
her, or
the idea of her?)
So in your piece, the decisions you make in terms of plot, character, and language should all contribute to some overall message(s) that you want to communicate.
I don't know whether I should tell it from Gatsby's perspective, or from Nick's perspective, or in third person.
See above. Work out what you want to say, and then backtrack from there.
If you're having Nick be unaware of Gatsby's fake-out, then telling it from his perspective might be somewhat counter-intuitive, which means that you couldn't adopt the "voice" Fitzgerald uses, unfortunately. Though perhaps you could have Nick trying to discern the clues and unraveling the mystery of the Great Gatsby. Alternatively, if you're writing from Gatsby's perspective, think about how you could make him a believable character - what does he want? What does he value? Why is he doing certain things and saying certain things?
Most other advice regarding creative writing will depend on the form and message you choose, so let me know if you still need help and I'll see if I can offer anything more specific
