I see... too bad 
Regardless, the previous line of thought regarding the calculation of the current limiting resistors for the LEDs has opened my eyes to an important fact: no matter what component here, the current passing through it will greatly vary (from 0.02A to 1.28A), which means that its voltage drop may also significantly vary. That means that if only a few LEDs are lit up, they will be brighter compared to the case when most of them are lit up. That's not good. In a LED cube all LEDs should have the same brightness. Inevitably, the question that comes to mind is: why are we trying to use 8 MOSFETS to switch the cathodes instead of using 64 simple transistors to switch the anodes? Wouldn't that be more simple and more cheap? Sure, they would take up more space, but we could use ICs like the ULN2803, which groups them by 8. Or am I wrong?
Thanks,
Andras