HI Prahlad

You did not required to have any opto coupller since isolation is provided by transformer, but instead of simply using reftifier and divider to match your signal it will be better if you use some "active rectifiers" constructed using opams. These type of circuits are normally used in multimeter for AC V & I measurment. Here you can be able to easily match the output signal with input by compansating the diode drop. For eaxmple if you match 460 V to 4.6 v that will make your calculations inside the controller easy.

Thanks
Santanu