Your future library must be based on statistical projections for 20 years from the date of application.
Public stakeholder surveys and meetings are often done by a professional Library Building Consultant. This has two advantages: the consultant has experience with gathering this type of data, and s/he is a neutral party in the eyes of the community. The MBLC can provide you with a list of consultants with public library experience (the list does not constitute an endorsement or recommendation of any kind).
You can also ask another library director to conduct the public engagement sessions.