PLEASE don't take this as a smartazz answer, but it sounds like the first thing to do is work on your heath. Loosing those unwanted pounds can help you live longer, since a heart attack is a much more likely enemy to prepare for than the two legged attackers you're wanting to train for. Your whole quality of life will improve, which will include your training/shooting abilities.
I'm not a nutrition/training expert by any means, but the basic gist of loosing unwanted pounds is to eat only as many calories as you're buring through exercise. Avoid foods high in simple carbs and excessive fats, and start moving around some more. MOST of getting with the program is mental. You have to want to loose the weight and keep it off, and once you do, diet and exercise adjustments become more tollerable and natural.
Please take what I'm saying seriously. I don't know you from Adam, but hate to see anyone miserable.