1) Yes that is how I fine tune the first layer print height.
2).525 is correct but steppers can easily be over driven by a lot. feel the stepper temp if it is hot to the touch you went to far, warm is were I keep it. Make sure you drivers do not over heat, anything about0.7v you will need active cooling.
3)vref*2 is for the a49 drivers the 8825 don’t need that. You can turn that z up higher if you are worried. If it is not missing steps it is fine, but turn it up to 0.7 and run it for a while and see how the z stepper feels.