Not only you, but also how good your instructor are when it come to teaching Martial Art.
No, exercise and diet do. Any physical activity is good for you but no single thing will do it. Healthy and fit (in shape) are not the same. You can be in shape or fit and still not be healthy. I am assuming you mean being in all around top fitness you can be. So a very very strict diet and very strict exercise routine will do that for you karate or any physical exercise would be a good addition to the exercise.
Nope. I have seen many Karateka who are sadly out of shape. It's all how you train. There are no guarantees. To get into shape you got to do the work and have a good diet.
No, it's the same as going to the gym doesn't mean you'll be fit. It depends on how you train and what you eat.
No it won't. "Karate player" I had to laugh
