We have the general circle, plus 3 others that really are distinct operational areas of the organization (even though everyone participates in them).
We have pretty good role definitions set up now I think, but one of the problems with a small organization is that if the owner of a role is on vacation, or out sick, or working just part-time, someone else usually has to step in and deal with situations.
Mostly I'm concerned about the Facilitator role. Acting as referee during meetings, he/she has to control the process. I see that as being difficult if that same facilitator is the one owning the tension, or affected by the proposed resolution to someone else's tension. Especially since we haven't officially implemented Holacracy, when we hold our first governance meetings they are going to be very clumsy, with the facilitator constantly blowing the whistle and explaining the rules.