Unfortunately between work and family troubles I don't really have the headspace free to contribute to a major homebrew project at the moment, and if I did then I'd be more inclined to revive my own previous projects if only to not leave them unfinished. The only advice I can offer is to try to get in some games with the current rules to get a feel for what is and isn't working already, and to look at the existing round of arcane journals to get a feel for what expanded faction rules look and feel like in the current old world system so as to craft something that fits in with the rest of the game.
I will say: The legacy vamp count rules are already pretty strong, among the strongest in the game (apart from maybe new Cathay, they seem busted but too soon to really judge). Even if the vamp count pdf isn't as fleshed out as we might like, or at least not in the ways we would like, take care when adding to it not to tip the result over the edge.
