and if so how often should you do it?
It does help to tone your calves and your glutes. Like all exercises it's about pacing oneself and not pushing it too far. If it starts to hurt then you are defeating the purpose of the exercise. Just like you would do say, 3 sets of 10, with weights. Then the same thing would apply here. Figure out how many times you want to tackle the stairs and stick with it until you feel comfortable to do more.
How do you tone the back of your arms effectively? I do push ups but they don't seem to help that area.