A great little one shot, one that deserves a follow up story. I think now that Harry has found his confindence, you could make him a little more independent of Fumblebore, but not a complete break. Keep him at Hog's, but make him into a strong and charasmatic leader, who is willing to do what ever it takes to get the job done...someone who'll study and train hard, but not push his friends away.
You probably don't have to use the old Horcrux story, as you never alluded to what Dumbledore was looking for on the night he was killed.
You've created a good oneshot, that would make an excellent fic.