There are no rules from FIRST on the number of mentors present at any given time. There is however a requirement for there to be 2 adults who have passed FIRST's Youth Protection Program screening. Sometimes that second person is not involved with the team on a daily basis, I know teams where the initial second screened contact is the district CTE director or a Vice Principal.
Your next step is to contact your local Senior Mentor which you can find here.
http://www.firstinspires.org/ways-to...senior-mentors They can help you through the start up process.