I used to work up full character sheets. Things like "favorite food" and "favorite color" were on them, among many many other things. I don't do that anymore, as I'm not sure they ever really helped.

Actually, I think the thing holding me back with these characters is how they relate to the ones that I already know pretty well. Because I thought it was going to be one thing, and now I'm thinking that will be harder to work in and might not make much sense outside of my head and/or won't make any difference to the story itself. So I think some rearranging with the various characters and how they all know each other and all that will help more than a character sheet or anything.

Plus, I have a general sense of them, and I think that if I just sit down and start writing them, they'll make themselves known to me through the writing. :)