Regarding longevity, this article points to a study that shows exercising 150 minutes a week makes a difference, but exercising 450 minutes per week is the sweet spot, where the benefits of exercising more than that don't help much. My own doctor said I should aim for exercising at least an hour a day with my heart rate above 100 bpm. Walking does the trick. http://well.blogs.nytimes.com/2015/04/15/the-right-dose-of-exercise-for-a-longer-life/
Now I actually think doing some exercise is beneficial, but it doesn't need to be much at all. And it may not help at all with weight loss. What you eat matters most.
I found this site interesting: https://www.aworkoutroutine.com/start-here/