Actor Allusion: Joanne's actress had previously played a vampire in the Twilight films; in this series she's incinerated by a character with sunlight powers. Additionally when female vampires in that series lose a loved one they tend to go on a Roaring Rampage of Revenge, slaughtering anyone associated with their loved one's death.
Promoted Fanboy: Zachary Levi was a longtime fan of the show, thanks to Chuck and Heroes airing together and having similar promotional schedules, as well as being friends with Zachary Quinto and some others in the cast. When the series was announced, he asked Tim Kring if there was any room for him, so Kring wrote Luke Collins for him.
The original cast only heard about the new series through the press release and Twitter. Only Zachary Quinto, Milo Ventimiglia, and Hayden Panettiere have been confirmed so far to decline reprising their roles. Tim Kring himself has confirmed that they, along with Ali Larter and Adrian Pasdar, will not be in the new series.
Original characters returning so far: Noah Bennet, René, Hiro Nakamura, Matt Parkman, Mohinder Suresh, Micah Sanders, and Angela Petrelli.
The idea of having Tommy and Malina be twins isn't a new idea to the show's universe, as Peter and Nathan were originally conceived to be twins. But due to difficulties in casting, Nathan was simply aged up. At least it's easier to cast brother and sister fraternal twins.