I'd recommend that you isolate ALL of 5V & 9V circuitry from the AC power line.
Anything that "comes out" (such as the USB connector) or anything someone can touch MUST be isolated.
If it's self-contained and enclosed in an insulated/isolated case it doesn't really have to be isolated... But that makes development/debugging/troubleshooting difficult and dangerous and it's just a bad idea for homemade/hobby projects.
It's probably also a good idea to by extra op-amp & ADC chips. It's always a good idea to have extra chips when developing a new circuit, and it's especially easy to fry stuff that's connected to the power line. 
Take a look at [u]OpenEnergyMonitor.org[/u].
...I'd recommend you start-out by simply measuring current. For "normal household/hobby use" the voltage is known and the power factor is nearly 1.0. After you get that working you can add voltage & phase measurements later if you feel it's necessary. And, the Hall effect device is isolated which simplifies everything!