Your question is too vague. What part of the e-commerce web site will be "Third Party", the entire web site or the database section? And or you talking the software is third party? In any case, you should have a detailed business plan to include: objective, scope, policies and procedures, business processes, organization (who will be using and developing), location, IT Infrastructure, etc.
Hope this helps..
Disclaimer: The above comments are solely the opinion of one person and not to be construed as a directive or an incentive to commit fraudulent acts.