If you are totally new to AS, I recommend you to go to some tutorials or buy a book first.
To give you a hint to your question, you create an Array or Vector with those objects and then use Math.random(). However, there are a number of points you have not explained here. What kind of list do you mean? Are these characters all different Movieclips in the library? The duplication question is a completely new question. So in one thread please ask only one question.