Hardware requirements for building a large nonprofit organization site?

What is the best hardware for building a site that would have initially 100 separate subsidiary organizations and each user would have access to all other folders for view and search purposes. Each user can upload only to their specific organization. I think we would probably like to have search capabilities by word in each document as well. If our idea works well we may want to expand out to 400 to 500 subsidiary organizations in North, Central, and South America. If we go to a world level we might be talking several thousand subsidiary organizations.