Um... honestly no CS for Servants is a really really bad idea.

I have seen people try to use horrible, terribly broken and canon-violating Servants when there [i]was[/i] signups and with no Servant CS it's incredibly risky.

I know it sacrifices the OOC secrecy but I feel like it's probably the best idea to do full bios for Servants. It makes it much easier to make sure that no-one tries to use someone who doesn't exist or use really broken skills or NP's. It's easy enough to catch people if they try to metagame using the CS's.