I would have thought that 100mb Ethernet was quite fast enough, as your broadband is only 38mb max.
Unless you plan to transfer very large files over Ethernet connected devices with gigabit ports, on your home network, the extra speed is not going to be any advantage, as the gigabit port will simply connect at 100mb.
Your home hub 2 does support port mapping and DDNS, e.g. DynDns. The home hub 3 fails to do port mapping.
You could buy another modem/router, but it would probably give you no advantage.
I believe the HH2 does have wireless "n", or that is what I was told.