What's the first step one should take when determining the amount of overload to include in an exercise program?

The answer is evaluating your present state of health.  Best way to do that is to consult your doctor and to see if you are fit enough for strenuous exercises.  The next thing got a gym have the trainer devise a plan to fit your health goals.  That way you will know the right type and amount of exercise you need to be fit.

which ever one is showing doing the same exercise in time intervals such as 30 seconds or a minute several times.