I kind of think you blew a wonderful opportunity to come up with something other than horcruxes but given that this is a few hundred years later maybe a nice Klingon Disruptor and a Vulcan mind-meld can solve Harry's little problem.
As for Luna's letter: I'm a bit surprised you used "Quetzalcoatl" but in a way it fits. I think we've already seen the plaque. I'm still puzzled about who "the fanged one" is though.
Regarding Hui (and girls in general), I hope you take your time with Harry's relationships and don't focus too much on them. I'll just paraphrase (more likely butcher) an old about the British navy. "Ensigns have girls, Lieutenants have fiances, Commanders have wives and Captains have a families."
Good luck with the next chapter!
Author's response
Not really blown a chance in regards to the Horcruxes, more of I have a plan that is going to catch a lot of people off guard.
One person has correctly guessed the identity of the fanged one. from a certain point of view, its pretty obvious, but you need to really think about it. once you do and figure it out, you'll smack yourself for not realizing it. Use Luna/Ravenclaw logic and it makes sense.
Harry's relationships will come of age in their own due course.