In most cases having two routers and double-nat probably works ok.
However from a "network perfectionists" point of view, ideally there would be one router on the LAN, and it would host the WAN IP address whilst feeding out LAN IP addresses via DHCP, with the addition of switches if required.
I douby Sky will care but about all that, and the new Hub will probably not have a modem only option. Happy to be wrong though!
Might be slightly academic though, as I'm not sure the Asus routers support authenticated DHCP over WAN anyway.
Oliver.