Hi!
I think there's all sorts of literature floating about to help you calculate MOSFET driver–circuit gate components, but from my experience with monitors and PSUs, etc., A series resistor of 10 R and a gate zener (if one is used) of 15V, 500mW with the cathode to the gate is a useful starting point!
Have a read of Peter Lenk's book, "Practical Design of Switcing Power Supplies" for useful design tips– I think there's PDFs of this to be ferreted out somewhere!
Chris Williams