Lets start by looking at how to assemble a team. The guiding rule here is to keep it small. Managing a team of people is a full-time job, even when all the team resides in the same building. If you’re dealing with an on-line team, you can easily spend all your time managing it, and that means you won’t be spending any time on making your mod. Adding more people to the team doesn’t mean more work will get done. The more people you have, the more time spent managing them. Team Fortress’s core team was 3 people. Counter-Strike's core team was one person.
When looking for team members, try to only hire people you absolutely cannot survive without. Your first instinct might be to hire anyone who can code, or model, or make maps, and so on. But for your first version, you probably won’t need more than one person for each area of your mod (code, sound, models, maps). You may not even need any new models, sounds, or maps. Don’t hire anyone until you’ve seen examples of their work. Make sure they’ve actually finished things. If they’re a modeler who’s done 20 models, but they’re all half-finished, you don’t want them.