Pulse transformer isolation on PCB
Regarding heat: I would consider 200 mA at 5V as low power. You probably don't need to worry about substantial heat through the coil, or need a ground plane underneath it. The only thing that might get hot would be the switching element (IC or output FET).

Regarding EMI: You're circuit probably has a large input cap (33 uF) and a large output cap (10uF) after the coil to stabilize the rails. If you are concerned with switching noise, it would most likely come from ringing. Use a few filter components after the output cap, but as close as possible to the coil. I generally use a 1 uF cap, 0.1 uF cap, and a ferrite bead matched to 100x impedance ratio of my switcher's frequency vs, the DC resistance, below is a link to one. If you are concerned about radiated signals from your coil, consider using a shielded inductor. For any signal traces crossing pathes with your power signals, try to make them cross at perpendicular angles, instead of running parallel, the minimize chances of inductance.

Ferrite Bead: http://www.digikey.com/product-detail/en/742792114/732-1621-1-ND/1639565