Although the idea sounds good on paper (no pun intended), the truth of the matter is, such a project in book form will no doubt take several years to finish, considering you want to cover everything the series has to offer in minute detail. a dedicated website is more feasable from a technical standpoint, but even that will be a daunting task and i feel it will just become a glorified Castlevania Wiki, which already exists. those of us that would say "sure i'll help!" will no doubt drop out early on or months into the project, either by declaring so or more likely, "disappearing" with no notice. I just don't think all the people that are willing to sign on will still be there by the time it's all "finished" (considering it gets that far), because we all have other responsibilities and are just unable to dedicate the amount of time we want to, or more likely, just become lazy and disillusioned with the project. Then there's the majority in the community that say "sounds awesome! let me know when you're finished." and offer no help at all. It happens all the time. I don't mean to sound pessimistic but it's true, especially with dealing with people over the internet. I know this doesn't apply to all fan projects of this calibur, but those are the exceptions and are certainly in the minority.
I feel the best bet is to find a core group of individuals you know personally and have no trouble with contacting them, that way ideas can get exchanged easily and a nice foundation. Or people you've known online for years (not just by their username/online persona, a genuine friendship), that you know won't bail on the project for whatever reason. Then gradually recruit whoever else that's willing to help (strangers on the forums, i.e. most of us). Perhaps I'm thinking too deep about this, but it's just my opinion on the matter prunyuu~