As many as the bandwidth will support.
IT will just get slower and slower the more people are connected.
it's possible to get the Home Hub to only allow wi-fi access by certain machines using the unique MAC address of a machine. The answer is yes, and here's how to do it...
Log in as Admin, go to Advanced, and go to 'Configuration' > 'Wireless' > 'Configure security'.
Then go to "Allow New Devices:" and set this to "New stations are allowed by registration", and press 'Apply'.
To add a new device, go to 'Configuration' > 'Devices', and there's an option to get the Hub to scan for available wireless devices. You can edit a discovered device and assign it permission to connect via the Hub.