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.