Building smps- pwm isssues
How about a 2 minute design review?


Make sure the primary size of the transformer is properly fused. Also include a common mode choke and L-N filter cap for conducted emission suppression. You can get that all in a single package, and I would recommend that for this project. 
0.012F is a big cap. Some inrush current limiting may be necessary.
At 400kHz, you will need a gate driver. Usually it is powered from the rectifier side of the switch. You don't show what your turns ratio is on the transformer, but make sure the gate driver's absolute maximum voltage rating isn't exceeded. The gate driver should be able to accept 5V TTL input from your microcontroller.
Your microcontroller will need powered from the same node as the gate driver. Assuming is a lower power relative to your load, a linear regulator should be fine for that. 
As FakeMoustache said, you want a P channel MOSFET there. There are dedicated gate drivers for driving a P MOSFET in that configuration. Further, you may want to consider synchronous rectification.
If you're putting this on a PCB, which you should, layout will be critical.