Post History
It really is up to you which you write. However, I would recommend based off of my experience writing a short story first and then if you are still feeling good about the idea try and expand it.
Answer
#3: Attribution notice added
Source: https://writers.stackexchange.com/a/20478 License name: CC BY-SA 3.0 License URL: https://creativecommons.org/licenses/by-sa/3.0/