If I am not careful, I will soon earn myself a reputation of harping on "good starting points" that have limited value in exercise.
I'll throw caution to the wind, I guess.
3 sets of 10. 20 minutes of "cardio". Stretching after exercise. Stretching before exercise. Stretching at all - yes or no.
Trial and error is a great part of the foundation of progress in any endeavour.
Here is something you might not have considered in the trial and error paradigm: the greater the trial, the greater the potential for and magnitude of error.
One set of 10 (or even less) might be more justified as a starting point. If your response to that is something like "What's the point?", then ask yourself why you showed up to exercise in the first place.