consider using a barbell? I just started stronglifts 5x5 and it uses full body workouts with progressive loading, adding a set amount of weight to the bar each workout and exercise. You start with just the bar. This allows you to track progress and full body workouts are the best for fat burning. I realize this is a heavy lifting program and can be kind of intimidating. But the idea of progressive loading is good because you don't start too heavy and you don't get burned out. If you are trying to lose 80lbs its going to take time anyways. Just try not to do too many exercises as things can get complicated and focus on say 3-5 exercises that are full body. I don't like machines because they isolate, aren't natural movements, and don't force you to balance the weight. Good luck to you and hope this helps.
P.S. walking is great too. It clears you mind and keeps you moving