10KB is fair and should allow for some interesting avatars. I think it would be nice if avatars represented figures with at least some relation to the theme of the board. Not necessarily a strict one, so things like Rommel or Napoleonic era figures would be fine, but perhaps not a bunch of flowers! For a number of reasons I think it would be best to restrict the url avatars to those uploaded to the Org servers. If that were the case, I'd have no problem with newer members having them.