Okay. Personally I think you are skimping on some interesting challenges that Harry could have faced during his fifth year. I would have loved to have seen a war of wills between Harry and Umbridge. I would have liked to see more interaction of Harry and the other characters. I would have been cool to read Harry hearing about Neville's parents and then have him REALLY stick it to Bellatrix.
As for the battle scenes, I thought they were good. A little bloody, and almost violent enough. ;-)
The idea of siphoning power has been used before and it was a theory that readers had a while back, prior to book 5. I've always liked it, and prefer that idea to the Horcrux idea.
As for relationships, I'll guess you probably have a few "harem" votes. I can see how that fits into a vampire type story - they seem to go hand in hand. If you go this route, I suggest you pick one or two standard characters and several odd ones. I could go for a harem as long as some the participants are "unusual". How often do you see harems where women like Narcissa, Rosmerta, or Tonks are used? You could use one or two others such as Lavender, Cho, Angelina, Alicia, or Katie. Can you imagine a harem consisting of Hermione, Pansy, Narcissa and Luna?
You've sort of already laid the ground work for something with Hermione in chapter 8. I think Harry would turn Hermione because he has his own reasons. Just as she wants power and such from turning, he would gain something from her. Perhaps before he turns her, she asks him what he gains from the turning. Or perhaps, he asks her what she offers. In any case, I think this type of dialog would be interesting to read.
One thing I will say, Harry has to get past Sophia. Three prostitutes isn't going to do it. Hermione might be able to provide what he needs.
Yeah, I'm leaning towards Harry pairing with Hermione. I wouldn't make it too romantic - I don't see either of them being mushy. I do see them creating an honest partnership where they do love each other.