A flywheel inertia dyno should still give the same general results regardless of what flywheel you use - the torque and power output of the motor should be the same. The difference will be in how quickly it accelerates - too light and you won't be able to capture enough data due to the sample rate limitations, too heavy and you might burn out the motor or sensors with prolonged high current draw.

Turbo and boost affect the timing of the motor. Boiling it down very simply, it's the same thing as adjusting the endbell on the motor but doing it electronically. So it's really just altering the parameters of the motor, rather than "pushing" more power into the motor. I'm not sure how familiar you are with the concepts of electricity, but in general a power source (ESC in this case) provides a voltage, and the load (motor in this case) pulls a current that's dependent on the input voltage and the parameters (resistance/impedence etc) of the load. Pretending a motor is just like a resistor (it's not, it's way more complex), Ohm's law says the current is voltage divided by resistance.