Approach for building local/city versions of a national website?
I'd recommend the Domain Access module(s) as the easiest way to set this up with multiple sub-sites (even with sub-domains) but still having a central site to control content and access:


  The Domain Access project is a suite of modules that provide tools
  for running a group of affiliated sites from one Drupal installation
  and a single shared database. The module allows you to share users,
  content, and configurations across a group of sites


It comes with a dozen or so helper modules and a few stand-alone projects that make it easy to create and manage sophisticated site networks.