Logging 3-phase power
I will multiply the rms voltage and calculated current to arrive at power (and then throw in I^2 R to account for the power lost in the resistor?)?


AC power is more complicated. If you multiply like DC, P=U*I, then you know S, the apparent power in VA. You have to multiply S with the phase angle φ to get the Real Power P in Watts. 

I suggest you read the AC power wiki page, and use those formula's to compute your values.

Since you can sample all required 6 channels (voltage and current per phase) at 10 Khz you should be able to get at least some accurate results. However, your buck/boost might cause an inaccuracy in the measurement due to distortion.

You will be in for some serious software work though.