All it takes is 3 people. Find a place that has the room for the group to grow. Find people/quilters who want to meet other quilters and are welcoming.
Even if you meet in someone's home at first. Start and see how it goes.
If you are opening a store let the class area be the group meeting place at designated times. Be aware that there will always be detractors, so don't expect the new group to be your source of business for your quilt shop. Have fun with it.