With respect to the stories, the method I've been taught is that your programming team typically works on a two week cycle.

Every two weeks you have have a meeting with the customer. At this meeting you go over what has been completed. The customer then hands over the next set of stories and you only accept the amount of work you know you can do in two weeks.

In this manner you never have all the stories, you only work in the here and now.

There are more things to be taken into account here, but I won't bother with them at the moment...

Cheers!