Mike - good post, overall a solid plan. In an organization of any size, quite a bit of social media use is already happening, possibly "under the radar" with no formal coordination. So a couple of key pieces to a a strategy are drafting a social media policy for the organization (the master list of "shoulds and shouldn'ts" as well as "musts and mustn'ts" for social media use within the company) and an inventory of what's already in place (I spoke to one billion-dollar company where HR had set up a company Facebook page; the marketing group discovered it only through an external audit).
Also, make sure to update your stats. Facebook now has well over 800 million users. Twitter has close to 500 million total, though only about 100 million are classified as "active" users.