You cannot measure this with a DMM. Since it is strobed with a higher voltage than the lamps are specified for the lamp glows normally or a bit dimmer. It is basically a short pulse, each column of the lamp matrix at a time. Theoretically each column will be active 1/8th of the time. It will be too fast for a DMM. And since the voltage is no sinewave it also depends on the type of DMM. The cheaper versions may perhaps only detect sinewaves. Other DMMs also measure non-sinusoidal waveforms.

How fast it is depends on the processor speed and its program. Normally the matrix is 8x8 for whitestar. 500 per second can be true, but to be sure the best thing would be to measure with a scope. I wouldn't believe everything just because it is written somewhere.

Current depends on how many lamps are on at a time in that column. Again: these are pulsed currents, and too fast to measure with a DMM.

Best thing to do is measure with an oscilloscope.