I would take every business class available, along with ASE automotive classes.
You can be the best mechanic in the world, but it you cant manage your money and employees, you'll be out of business in no time.
You dont mention where youre from, but each state has its own division that manages auto repair facilities. Check with your local Secretary of State or DMV for licensing requirements and business laws governing auto repair.
Save your money, fresh company startups requre a big bank account, you have to be able to cover all your expenses(employees, benefits, utilities, insurance, licenses, building, tools, etc) for at least a year to insure time for you business to take off. Trying to earn as you go can cost you good employees and customers.
You have several years before you could legally enter into the contracts needed for such a business, so spend those working in an existing shop learning how they should and should not function, plus plent of schooling to give yourself the best shot at succeeding. Most of the cars you'll be working on will be newer stuff, so learn about fuel injection and electronic controls, theyre not going away.