Mainly streamline the RP; seriously, at maximum optimism, you will get a dozen or players taking up the mantle of multiple PCs. DSM is, strictly speaking, not as popular as BL, nor does it have as many members registered, and not all those who *are* care for rehashed vanilla Grail Wars.
I'm not a GM, so I can't speak w/ any real authority on the subject, but making a large player roster and expecting to be able to fill it up for something like this seems like baiting stagnation. I'm not gonna say "Do one like Alf's RPs," but I *would* implore for some increased verisimilitude; maybe try something like an AU Hollow Ataraxia that's closer in presentation of drama and action like the original Melty Blood?