This step is simple (as simple as they come at least)
Write the story!
With all the previous steps, you can now progress to this step, and actually write your story!
The reason why this is a simple step is:
1 - you have your idea
2 - you have a thorough knowledge of every aspect of the topics in the story
3 - your characters are "real people" - even if it is only in your mind
4 - you have the music to inspire you in every scene
5 - you have your plot planned out thoroughly and
6 - you have your dialogue ready.
See? Simple :)
Now you've got to write.
Set a yourself a minimum word count goal, and stick to it. If your end word count exceeds your goal, good, but DON'T STOP WRITING until the story is finished! DON'T RUSH IT! Often writers get so excited about writing the ending, they rush the last few chapters, which often results in plotholes. Massive ones.
Take your time, don't rush it, and finish in the same style and pace as when you started. Don't mix your tenses, if you start writing in past tense, stick with it, unless its a flashback... (CONSISTENCY is key!)
Most of all, HAVE FUN!