Controlling a power supply with a MOSFET
Almost.  You need a resistor from the gate to the source to guarantee that the FET turns off when the switch opens.  There is almost zero steady-state current in the off condition.  For the on condition, the lower the resistance, the less noise pickup that could lead to false triggering of the MOSFET, but the higher the power dissipation.  Consider 1 K, 1/2 W as a starting value.
A common rule of thumb for long-term reliability is 2:1.  Devices should be rated for a minimum of twice the conditions they will operate in.  Examples:
12 V circuit  --  30 V FET
5 A load  --  10 A FET
0.144 W dissipation  --  0.5 W resistor