I'm 3 weeks into STS for the first time, and before I started I was really intimidated. But I am loving it!
One piece of advice: take the time to do 1RM testing, at least for the exercises on the first 3 disks. That helped me to start at the right weight - challenging but not hurt-myself heavy. I've been sore but not in an injured way, just some good DOMS. The body weight only exercises (especially push ups!) will be challenging enough, so it was good to know that I was, in fact, starting at 60% of my 1RM like you're supposed to.
Good luck and have fun!
edited to add: I agree with the advice to modify if needed. I'm doing all push-ups on my knees, for example.