All you need is to install HC on Exchange server 2007 or 2010 machine containing the role of HUB Transport Server and HC manages the rest itself. In case of Exchange 2013, HC should be installed on the CAS Server. It monitors and handles all the Exchange 2007, 2010 and 2013 roles for you in an efficient and organized manner. There isn't a long list of steps to install HC with Exchange 2007, 2010 and 2013, all you need to do is:
During this process all Mailbox Servers and Client Access Servers (CASs) are shown to you. Here you just have to select one CAS Server for Outlook Web Access (OWA). That is it!
As your business grows, you may add new CAS, MBX or Hub Transport servers to your Hosted Exchange and scale up on the fly.