So far, your chances seem pretty good. 90 percent of cadets at West Point have a varsity letter, while a majority have two. You probably want to make it a goal to earn at least three varsity letters, so look into something other then track that you might be interested in. Also, look at some of the sports you can participate in at West Point, it would be advisable to play this in high school if you want to advance to the West Point team. Your karate belt is also great, and the requirements for black belt will certainly be important where leadership is concerned. Also, start doing some training for strength. Nerd Fitness has some good beginner and advanced body weight circuits you should look into doing. Endurance and strength are important to ace the CFA (Candidate Fitness Assessment) which you can also take at SLE (Summer Leadership Experience), or West Point’s summer camp.
USMA puts a huge emphasis on engineering in order to promote critical thinking, so those workshops will be helpful. If your school has an economics class, I suggest taking that. Other then that, your courses are putting you at an advantage, as West Pint suggests taking calculus, government, and other lab based sciences. AP chemistry is very good. Try taking an AP calculus or other advanced math class, too. The average West Point GPA is approximately 3.75, so yours is very good. However, start practicing for the SAT/ACT now, and remember that USMA takes your super score, or the combined value of your best scores in each section.
A majority of West Point cadets were in NHS, and many attended Girl/Boy’s State, so these activities are certainly good for your application. I don’t really know about Link Crew, so I won’t comment on that. If I were you, I would try to put in more service hours and get awards for those. For example, I plan to have my Girl Scout gold, silver, and bronze awards by my sophomore year, and I have the President’s award. (I have gained the bronze and am currently working towards silver.) Also, look for leadership positions where you do volunteer or work.
Make sure to apply to the aforementioned SLE, and tour the campus. These things can familiarize you with the way of life, and your name might even be recognized by admissions directors. Also, start contact with those who can get you a nomination, and your admissions liaison. Make sure you come across as respectful and intelligent, a person who is different and dedicated. Make sure your name will be recognized, and not just one of the masses of kids who apply for nominations every year.
Full disclosure, I am only an 8th grader, but I have done extensive research on this process and hope my age doesn’t discount to you what I have written.