What’s the H/W and S/W requirement to Implement HOSTED OCS?

I am just wondering
what’s the Software and Hardware requirement to implement HOSTED OCS not the normal OCS requirement?
like (Web Hosting , Hosted Exchange and Microsoft Online Services)

And I want to know the maximum Users allowed to join the hosted server for each one single server?

Otherwise
What’s the preferred bandwidth to implement that for the Traffic performance?

Thanks a lot