This is the place to post questions and discussions on usage and style. The members of the Wordwizard Clubhouse will also often be able to help you to formulate that difficult letter.
"Windbag" is the closest noun I can think of, although it (and it's counterparts gasbag, blowhard, bloviator?) are more about someone who speaks at great length but really says little, of substance. There are a lot of humorous descriptions for the person you refer to, that follow the same format as "all talk and no action". All bag and no groceries, all foam and no beer, all sizzle and no steak, all mouth and no trousers...ACCESS_POST_ACTIONS