Odds of Hanging On
This is the tricky bit. The work will rarely be steady, so you're hanging on pretty much day by day. The idea is to keep jumping back up every time you fall down. But you should be good at that, considering your line of work.
Also, you won't be able to do this forever. Most stunt work is performed by the young and healthy—what will you do when your knees no longer want you to jump out of third-story windows?