For energy metering it is quite common to have your circuits GND connected to the mains line neutral. The whole meter is then put into a suffiently isolating box, and any I/O is done in an isolated way (by photocouplers or some IRDA-like optical readers, or with todays IoT madness, using bluetooth or WLAN).
For your application, well, it depends ...
I wouldn't isolate the metering chip from the uC, rather the uC's I/O from the rest (say like a CAN bus or RS458 line). There's a lot of ready made solutions for RS232 / RS485 and alike by e.g. Linear Technology, or CAN isolators by Texas.
If you go for a rather complex or non-standard interfacing from your uC to whatever your host is, one could imagine to isolate the meter chip from the uC - there's quite a few solutions for this, like photocouplers, digital isolators (ADUM..., ISO...) or complete SPI isolator modules including an isolated power supply by Linear Technology
And yes, you'll want an isolated power supply for the isolated part of the circuit, if this isn't a high volume commercial project, I'd go for some ready made solution (like a AC/DC or DC/DC converter), there's plenty of them. Watch out for the required isolation rating.