The DOCSIS modems have a configurable CPE (IP addresses), if its set to 2, it will lease 2 IPs without needing to be power cycled, If it is set to 1 In order to connect a 2nd/different device, either have Shaw add the 2nd IP, Or power cycle the modem to release the IP/MAC address the modem has in the ARP cache - Going this route, you can still can only have 1 active IP from Shaw.
The Terayon modems have no IP limit - can pull as many as you want.
Its not a memory thing in the DOCSIS modem preventing you from getting more IP addresses, it's the config file the modem has, specs from Motorla say that the modem will support 32 IP addresses, Shaw's system has a maximum of 8 IP addresses, but a residential account only has 1 or 2 included in the price.
10Mbps hub, unlikely to see a speed change on just HighSpeed, Extreme, yeah, you'll see your speeds not get as fast as they could. The other thing to consider when using a hub is you don't have full-duplex traffic, so you can see a speed drop from that as well, more noticeable on Extreme.
Kevin