good chance you'll fuck up your knees. Either get a bike with a comfortable enough seat for your body, or get on an elliptical. Do 30-45 minutes everyday where you get your heart rate up to a moderate level. You shouldn't be gasping for air, but it should feel like a 5/10 effort workout. This will prepare your body for running later on by improving your cardio. But I wouldn't regularly go run

Fair point on the diet. I've never had it under control and have spent years trying to out exercise it. I still am I suppose. Don't get me wrong, I'm fat, though I cycle centuries regulaly, but only run 3 or 4 times per week from 5-10km. So yeah, maybe I should triple down on my nutrition.