I'm wondering if there have been any speculations on the potentially realistic physical composition/metabolism properties of vampires in the canon or this fanfic.

Off-hand, the canon description is consistent with the vamps consisting of mostly carbon nano-fibers, with the sparking parts being traces of carbon in the diamond form. The conversion process appears to be a form of virus-based DNA rewriting. The metabolism could be based on catalytic cold fusion, with blood acting as a combination of a catalyst and a power source (human blood is a better catalyst).