N channel mosfet gate-source pin distance
The gate and source pins should not be more than about 20V or so different but this is  device dependent, check Vgs (max) in the datasheet; the voltage rating you are referring to is Vds (drain to source).

There is a calculator avaliable; for IPC-2221A, the 600V (DC or AC peak) clearance is 3mm (minimum).