Metro is one government and the collar counties are four, so your site needs five stories
Nashville and Davidson County operate as a consolidated Metro government while Williamson, Rutherford, Sumner and Wilson do not, and one page titled after the city flattens all of it.
Search follows the jurisdiction, not the metro brand. Someone evaluating a site in Franklin or Brentwood is dealing with a different government, a different review process and a different occupier profile than someone looking in East Nashville. Practice differs by jurisdiction and is generally worth confirming with the local planning or building department before you rely on it. The fact that it differs is exactly why the content works.
Build county as the top level of your structure and asset class underneath it. A Williamson County industrial page and a Davidson County industrial page pull different companies and different phrases. Neither one eats the other.
Use submarket names in the body copy where those are the words people actually say. Murfreesboro, Mount Juliet, Hendersonville, Germantown, The Gulch. Same vocabulary as the emails you already get.
The common failure is a services menu: office, retail, industrial, investment sales. Four pages, no geography, nothing a search engine can place on a map.