I think the first thing is to have a realistic target to work towards. What could you see yourself as being like at your best?
Essentially, losing weight and gaining muscle are two different things, and after a certain point, mutually exclusive. You can even end up fat and very strong, or light and lacking any muscle mass. People have naturally different body shapes that will influence how you look (limb length and torso length), so factor that into your realistic self-perception. I have a long torso, so whilst I have nice shoulders, I look ridiculous riding a horse. Similarly, different activities, like certain diets and certain exercises, often favour one body part over the other; if you do a ton of cycling it will help you lose weight and won't bulk up anywhere except your thighs.
If you want to bulk up all over, get to the free weights! Squats and deadlifts are the most efficient way to gain muscle mass, in a way that is reasonably distributed across your body. Don't expect a miracle turnaround however, as you'll only try to lift too much in one go, strain yourself, put yourself out of action, get less fit and lose confidence/interest. Doing that regularly (3 times a week) for a few months and you'll feel the difference. If you don't do anything else though, you could easily end up as a strong and fat man.
Weight loss is best achieved by cutting out snacking, alcohol, soft drinks and juices, fries. Most of these can be replaced with something as filling and healthy (though admittedly more boring): cups of tea or water, fruit, boiled potatoes. I find dieting and calorie monitoring to be miserable, but it is a continuous commitment. I've invented arbitrary rules, like reducing my alcohol intake to specific days or avoiding meats on the weekdays; even if you don't 100% commit to a diet, these rules make you mindful and give you a chance to say no to unhealthy things.
I don't know about supplements, but without getting into a regular fitness regime and diet to the point where both become a habit, any such thing would be a waste of time and money. Getting the right amount of sleep, sunlight, exercise and diet will keep you as sharp as anything.