Hi
We will also have one site doing what you have suggested, but we built one local site in our city while we worked on the business plan for the rest. That site has been live for 6 months and as we used the location for google local business and verified it our local site gets about 500 unique visitors a week from the local area (for free) which gives that location more than enough business. To get the same from adwords would cost £175 a week. We wanted to replicate this covering the country.
As for the updates, Wordpress Multisite you can set up a master site that can propagate all the changes into the others automatically
Mike