Username: Enyo
Favourite H.P. book/movie, and why: My favorite book still the Prisoner of Azkaban, because we discover Sirius and Remus in it, and I loved discovering about the Marauders, and about Harry's parents and their past. My favorite movie is the Order of the Phoenix.
Favourite Character: I have many. Luna, Fred and George, Remus and Tonks, Neville... (By the way, JK Rowling, WHY did you have to kill most of my favorite characters?)
I LOVE HARRY POTTER!

I'm also answering your last question
Delphi being Bellatrix and Voldemort daughter didn't surprise me that much. It's implied in the books that Voldemort and Bellatrix have a more relationship which is not a regular relationship between a leader and his subordinate, but almost a (unhealty) romantic one. Bellatrix is obsessed by Voldemort, Voldemort likes her loyalty and the power he has on her.
But I find them having a child a bit cliche.