In general, you do not need a specific license to conduct business online.  However, serving overseas customers can involve tricky questions of domestic and international tax law.  Sit yourself down with an attorney and an accountant who are familiar with the ramifications of doing business with foreign customers.  Do not skimp on their services, and be prepared to open your checkbook.  There's no hard and fast answer to the question of "which business form" -- it's a decision that needs to be made after discussing how you intend to run your business, who will own it, and your projected income.  Once the business is formed, you will likely want to obtain an EIN for the entity.