Meaning is the od finished and script planned out for the actors to follow.
If not then it might be a little early to start lining up acotrs.
I got the same probelem (especially fro Live action actors!) Just to damn early to advertise (I got to get a projector first for anime/and cg interaction with people (and build a cockpit and a bridge Muhahaha)

Get your mod team together (if you need one). Show some screens of your mod in action. Write a script for the basic things you need covered (even if it's just an outline for now of roles you need to fill for main characters: Like command HQ, comm officer, flagship co, wing commander, ect... the lines themselves will come later as you write teh story for the mod missions. Though now is a godd time to start thinking abut how you want your story to flow and what kinds of events you want to create , who will be involved, and what outcome you are aiming for as teh end result. ) Hope this helps you to get your needs across for voice actors, that way you don't get bombarded with 20 million questions about V/A... L8tr!;)