Do I need any special authorization from the County or City to organize bike nights?

First, the owner of the parking lot may have to approve. If you are using their space and not all persons are using the store or restaurant they may object and that may be tresping. Second, depending on whether you intend to have a group "ride" you may want to consider whether the ride will be considered a "parade" or some type of "group march" (like a protest). In that case you generally have to give local authorities notice (24 hours..etc) and in some cirstances pay for additional police to direct traffic. I would contact the local police liaison and possibly city hall for more information.