A snubber is used to protect the transistor from too high Vds, reduction of unwanted emission and to divert some of the switching loss from the transistor to a resistor.
If the snubber across the primary winding assures that the transistor is happy, you don't need an additional snubber or clamp across DS. In case of large physical distance between snubber across primary winding in combination with high dI/dt, you may need some snubber action close to the mosfet.
Vds voltage, I think you should need to have some margin to handle input voltage variations, inrush/transient phenomena etc. If you can reduce Vds max (with sufficient margin left), you can do that. Mosfet performance (think of Rdson) is better for low voltage devices.
Reducing leakage inductance is a combination of selecting the correct core material and using interleaved windings. interleaving increases the capacitance between primary and secondary.
Modern ferrite material can accept higher flux density at certain power loss, resulting in less turns, hence less leakage inductance.