Aside from the technical challenges of running a system with such a massive amount of data:
translations (left to right text and layout: https://sy-sy.facebook.com/), different laws depending on jurisdiction; for example privacy/moderation/takedowns, taxes/payment/invoices if you are selling anything, accessibility
If you ever start a company and you have the long-term goal to offer your service in multiple countries I would advise you to launch in at least 2 countries, preferably supporting different languages.
