It is even more important that the steering committee be prepared to share why they believe an association is important and why at this time. Do not be discouraged if the attendance is not what you hoped for. For every person attending, you can be sure 2 or 3 are wishing they could come. Keep organizational structure simple - a steering committee with a convener, a secretary, and a treasurer is probably enough to start with. You will want to relate meeting times of the steering committee and the larger membership to the goals of the association.
Some associations invite the bishop to be a member and attend meetings.
Others find it more helpful not to have the bishop involved so directly. You know your diocese and bishop. However, it is a good idea to keep the bishop informed of what is going on from the start so that there are no secrets or fears, and that the bishop can be made aware from the beginning that a healthy clergy union means healthier clergy, which is good for the diocese.