Check this out.
http://www.metrompg.com/posts/pulse-and-glide.htm
That answers most of your questions. I'm not sure about the Prius, but on most cars with power steering, it gets much harder but not impossible to steer with the engine off. This is because the power steering pump is driven by a belt from the engine. It is important that while gliding, after shutting down the engine, you turn the key back to the "On" position, not leaving it on the off or accessory position, since this may lock the steering wheel.