The default unlocked state of the Huawei HG612 will be to act as a bridge on LAN1. The Asus router will handle the Internet connection, which as long as it supports Sky's authentication method (DHCP option 61 I believe), you will have no issues.
In order to get stats off the modem you will need to connect an ethernet cable to LAN2 and give the PC connected a static IP of 192.168.1.x (x being anything except 1), with a subnet mask of 255.255.255.0 and a gateway of 192.168.1.1.
It may have one in theory, but if it does it isn't enabled by default. As there isn't an official way to access the modem settings there'd be no way to configure it.
No it is enabled, it just isn't used when the modem is in bridge mode.