This sounds like a great opportunity. If no one knows what your job is and no direction, then you have a lot of leeway to make it what you want.
I took a job with the same title for a small town of 55,000 about a decade ago. It was a brand new position for the town. My boss and council had some general ideas of what they wanted from me in the position, but no clear direction on how to get there. I found a great first step is to meet with each department you are to serve (Public Works, Planning, Police, Fire, Parks, etc...) and find out what they want from their GIS, what do they currently have for data and personnel, and get a feel for each department's workflow needs and limitations. In doing so, you can make allies, likely discover personnel who are already using GIS in some capacity, and develop a strategy that targets specific, quantifiable needs. This greatly helps secure buy-in from those departments, which is critical for success.
Good luck!