IIRC, the Oncore has an antenna power up transient of 100mA. I'm not sure if that's factored into the 0.9W figure quoted or not. Probably best to assume not, and allow for a 300mA worst case current draw.

The Oncore is TTL level CMOS. That means that the pins are not protected in any way, and as such are susceptable to damage from overvoltage conditions (and static).