Three years is a bit excessive. While it, in principle, sounds like a great idea, you will be fighting against memory degradation while studying inefficiently. It is best to save your exam resources until closer to your exam date so you do not waste them. HOWEVER, what you can do is do what Shreyas suggested and create an extensive Anki deck for reviewing every topic you learn so you retain the information "perfectly." Also, if you are made out of money, you can try Firecracker for MCAT preparation. One thing that would be a major advantage would be to constantly review old material throughout college. Most people forget small details from general chemistry, biology, etc. throughout the years, so doing this would put you way ahead of the curve because you will be able to rapidly retrieve information from your long-term memory effortlessly. If you couple this with reading articles (ACS, Scientific American, Cell Biology, etc.) and doing biomedical research, you will be able to integrate your knowledge into one beautiful picture. All of biology is ultimately chemistry, and all of chemistry is ultimately physics. In my opinion, being able to integrate everything into one glorious symphony will enable you to do extremely well on the exam (assuming you test well and know the patterns in MCAT questions through practice) while also allowing you to appreciate everything that you have learned.
You should also start your ECs now. Get leadership experience, go volunteer in a medical and nonmedical setting, and shadow doctors and get to know them. Like I said above, do research (if you are interested); you will be surprised by the opportunities that are available from doing research. If you do your ECs consistently and do them because you love them (not because it's 'expected') it will help you develop as an individual. You should also do some sort of hobby that is interesting. For example, you could perhaps start training in martial arts, play sports, or get involved in some sort of artistic endeavor (if you look around your city, you might find interest groups for music, pottery, painting, etc.). For all things in life, being interesting is positive. Adcoms (not just for medical school) like people who are interesting, enthusiastic, mature, yet also fun to converse with. Getting involved in some sort of athletic activity (running, weight-lifting, martial arts, sports, etc.) will also get/keep you in the best physical shape of your life while also fighting stress.
In short, I applaud your enthusiasm for the test. I can relate to that mentality myself. However, just studying practice materials for three years straight is unrealistic. Instead, you should focus on spaced repetition for reviewing old content in order to combat memory degradation while studying consistently (a few hours a day most days) for your classes and not just cramming information one week before your exams. Doing this will relieve stress, store more information in long-term memory, and balance your life with things that are enjoyable.
