Where do aurorae australis begin and in which direction do they move?
Auroras start at a distance of 80-200 km above the Earth's surface.

The color of the aurora will be blue/purple if the air molecules in the area below 120 km are excited.

If the air molecules in the area from 120-180 km are the ones that gets excited the colour will be yellow/green.

Above 180 km gives the red light in the aurora.

The most powerful aurora will in general be 180 degree from the Sun's position and it will move from east to west at the opposite side to where the Sun is.

During powerful auroras the aurora arch can easily cover 270 degrees or more if close to the magnetic poles, if the aurora covers the area away from the magnetic poles the aurora arch will get smaller.

When the charged particles from the Sun interact with Earth's magnetic field a powerful ground current will be induced, this can induce DC power in power lines and severely damage the AC power transformers. Should an event like the one that happened on September the first, 1859 (the Carrington event) hit us today we would have major problems with power supply and satellite communication.

You can read more about all of this here, Aurora and please take a look in the sources there too.