You shouldn't need to change anything, leave dhcp on the sky router, only traffic going externally using the default gateway will go over the power line as the rest will be on the same subnet?That's good to hear, my setup is a bit odd in that I use passthrough adaptors between the modem and router so I can have the router in a more convenient location without running cable through the walls.
Works fine with my current setup but will need it so the Sky router only sends a signal to the routers cable port and does none of the home network routing as the passthrough adaptors aren't quick enough.