How many story points should be in one sprint?
There is not a certain number of story points that the team has to have in a sprint but they do use their historical velocity, combined with capacity planning, to decide on the work they take into a sprint. The average velocity of the team is calculated as the average of the last 3 sprints and then it is adjusted based on the capacity planning (e.g if there are public holidays or annual leave it may be slightly reduced to cater for these). In that manner the team arrives at the story points for the upcoming sprint. That happens during sprint planning.