I've been twice now and still feel I have not done 80-90 percent of Iceland. I am covering some of the interiors this Summer so hopefully after the trip will feel like I have covered or semi covered Iceland.
With regards to auroras, you need a fair bit of luck to see them. Even when the conditions are just right (clear skies, cold, strong Auroral activity) so usually between Oct and March, the weather is so changeable that you may find yourself one eye on the roads and the other looking up for clear skies. Luckily for me on my last trip, I was with a guide that seemed to know what he was doing and even with cloudy skies managed to hunt down a faint aurora and turned into a stronger one moments later.
Here is the site I used to check for auroral activity (just select Europe)
http://www.gedds.alaska.edu/AuroraForecast/Also worth checking out my friends collection of Auroras which are some of the best I've seen around.
Northern LightsHave fun.