I would suggest you get some stuff ingame first, really. To attract other people, you have to convince them that what you are proposing is realistic to implement. Concept artists are a pretty key part of a TC or really any mod, but if you don't have any modelers or skinners to develop from the concepts, they're just pretty promotional pieces.
The best way to do it, I've found, is simply to start modding yourself. Make something people want to play. It doesn't have to be perfect, but give it your best, release often, and make it as polished as you possibly can. Anyone - anyone - can do a excellent mod without any extra assets, and even if you don't want to get into scripting, modeling is a great thing to pick up.