I think Harry is the missing Horcrux, it was his murder that was to forge the last one, but Lily's abjuration shattered Voldmort's soul. As to the Death Eaters trying to kill Harry, they probably don't know about the Horcruxs, in fact maybe Voldemnort didn't figure it out till recently.
Remember
"The one with the power to vanquish the Dark Lord approaches...Born to those who have thrice defied him, born as the seventh month dies...And the Dark Lord will mark him as his equal, but he will have power the Dark Lord knows not...And either must die at the hands of the other, for neither can live while the other survives...The one with the power to vanquish the Dark Lord will be born as the seventh month dies..."
As to Dumbledore's death, at first I thought he was faking, I mean with all of his power, but then I remembered his hand.....and with all of his power.
I think he was already dying.
I think Snape swore an Unbreakable vow to Lily to protect Harry and that is why he helps him and does not kill him.
As to is he evil, oh yeah !
But he is not going to be Voldemort's lacky this time, he is just waiting for his moment to avenge Lily's death and with Voldemort's final death, Snape can stop hiding. Considering his knowledge of Potions, why hasn't he written his own book? Because he could not risk coming out of the shadow of Dumbeldore.
I think Regulus Black is RAB, but if he is alive, it is only because Snape was the one who "killed" him. That would give Snape an extra edge.
As to the next book, I think Harry will try to do it himself and fail miserably, possibly loosing his owl in the process. He will be rescued by Fawkes and brought back to Hogwart's to recover. Then the team will unite for the final battle. Maybe the real Moody will be the DADA teacher next year. If the Order of the Phoenix is based from Hogwarts, that might convince the parents to send the children there, perhaps just for their safety alone.