The optimal weight for your individual body is not easy to calculate. The BMI-factor is from a medical point of view not a perfect measurement, it is a raw classification whether you are overweighted or not.
In general talk to your doctor before starting your workout.
With too much weight and wrong ambition you can injure your joints or stress your circulation. If you run slowly, you burn fat. So lose your weight until you feel comfortable (but don’t lose too much – you know bulimia!).
Watch during your workouts your heart rate, it shouldn’t go too high!
Sport alone is not enough to reduce your weight, it must be seen in combination with your nutrition. Read a book about LOGI or nutrition.