MOSFET switching dissipated power calculation
The switching times should be calculated by using the equations

tsw_on = (0.5*Qgs + Qgd) / Ig_on

and 

tsw_off = (0.5*Qgs + Qgd) / Ig_off

This way, you will obtain shorter switching times, resulting in lower power dissipation.  

There may be further errors in your calculations which I didn't review yet. When I am doing these calculations myself, I like to use Fairchild's Application note AN-6005.