A few thoughts and pieces of info about jury duty.
4) There are some people who will never be seated as jurors, because a competent lawyer will challenge them. The most obvious one is a police officer (current or retired). The prosecution and defense are each looking for jurors who can be manipulated and/or are likely to be sympathetic to their side.
5) An honest mistake about dates will usually not cause you problems, as long as you contact the court and get it straightened out asap.