Below you will find the invitation email text and Google Form I sent to potential participants. I chose to invite teachers that had 10 or more years of experience in the classroom. In my case I also invited teachers from all disciplines district-wide. This is a personal choice of who you wish to be a part of the group, but I found that the familiarity of being from the same district was helpful, but it was also good to have teachers that were not too familiar with each other or the other disciplines. This led to more enriching discussions.
My recommendation is also that the group not be too large or too small. An ideal number of participants may be somewhere in the range of 8 to 12 participants.
Also, if a teacher is not able to make all the scheduled meetings, then do not worry that this will make for an unstable group. I was happy to discover that it still was a productive meeting even if all the participants were not consistent. There were even some participants that enjoyed it so much, that they brought another teacher friend with them to the next meeting.
You may be wondering what to call this group, I suggest you let the group come up with their own name. My group decided on the name "Teachers Anonymous" after they decided they like the format of the support and confidentiality the group provided.