The character you describe sounds an awfully lot like a stock character in theatrical productions in ancient Greece, during the days of playwright Aristophanes . The character was called the alazon, the man who overstates his ability, as contrasted with the eiron, who understates his ability. (The etymology of the English word irony goes back to eiron.) See http://en.wikipedia.org/wiki/Stock_character.
A modern (and timeless, albeit dated) example of these two stock characters would be Sheriff Andy Taylor and his deputy Barney Fife from the television show "Mayberry R.F.D." If you watch an episode or two of this classic TV show, you'll be able to tell pretty quickly how the Barney Fife character (played by the late Don Knotts) fits the person you describe, almost to a T.
Deputy Fife was a harmless soul who was officious, legalistic, slightly boastful, overly confident (though timid at times), a bit vainglorious, and proud. At times he bordered on being deluded and lacking in sound judgment. He certainly meant well, of course, and had an endearing way about him, which caused people to like him and to put up with his shenanigans.
Perhaps one way Barney is different from the person you describe is in Barney's willingness to venture forth, usually half-cocked, determined to accomplish what he set out to do. Usually, however, he falls flat on his face, and good ol' "Ange" (as he frequently called his boss, Andy) would have to talk some sense into him and/or come to his rescue. Funny stuff. Not gut-busting, mind you, but good clean fun.
Alazon. I wish I had a more up-to-date English word or phrase for you, but I do not. Sorry.