How can I prepare for a medical career?

Honestly, it sounds to me like you are already on the perfect path to achieve your dreams. It's rare to find a 14 year old with your level of intelligence and drive. Everything you are doing so far will absolutely lead to your dream. You may want to find out if there is any volunteer work you can do when you have some spare time. Volunteer work, especially in the field of medicine, will always stand out on resumes and college applications. Good luck with your ventures!