I personally would vote for teams of four. Last I checked, we had the proper number of people for it to work out evenly. I think four people is a nice balance, as it basically ensures that about four people will always have an excuse to interact, and offers diversity in that interaction as well. On the other hand, having teams of only two means that we'd likely end up with a lot of back and forth, and if one player can't log on for a while, their partner is up the creek without a paddle.

As for naming themes... Legendary beasts could be cool. Maybe named deities from Greek mythology or some such? I'd say chess motifs, because I [i]really[/i] like chess motifs, but they don't work that well for team names. "Team Knight" or "Team Queen" doesn't really sound right, y'know?

Because I'm curious, and I apologize because I'm sure answering these questions is a pain XD, have you thought about how teams are likely to be decided?