It involves huge cost to register a trademark internationally.
Your first step should always be to register your trademark in home-country. This wold be your base to international application.
Then after, consider which are the prime countries you would want to register. Assess the cost for registration in all countries vs such prime countries.
Based on scale of your business and cost involved, you are required to opt for the best option for you to register a mark.
Important: e-Commerce business might require protection under multiple classes, therefore, during assessment, take all such parameters in consideration.
Here, the best option would be to consult a trademark attorney instead of finding answers over web. Based on case, an attorney would help you find the best way possible.