T5Nitro - You can see them that far south. In fact, there was a solar storm (maybe in the 60's) that was so huge the Aurora was seen as far south as Mexico! There is basically an auroral ring (like a crown with a fat rim that "sits" above the earth). As stated, it can expand or contract based on the activity. The more it expands, the more likely people south of the Northern Latitudes will see it. Red is rare, except at lower latitudes for some odd reason (I think because of the curvature of the Earth you southern people are actually seeing the higher altitudes of the atmosphere) and there is more of (oxygen, or nitrogen) gas that creates the red. Though, most of the ones seen from the southern latitudes will lack the distinct rays and curtains we get up here. Ends up being more of a diffuse area of color
Anyway - ah, filters. I only use a polarizer now a days (and I have a few lenses with UV filters as protection but I have slowly been removing them too). Polarizors are great for bringing out colors that are already there but masked by glare or haze.
I used to use a graduated ND filter when I was shooting film. What I always hated was that you get underexposed areas on anything that was over the horizon line that overlapped the brighter area you were tryingto hold back (like trees, or mtns). I attached a pic.
I drew the filter edge so you can see where it was. I moved the filter up and down slightly to hide the transition (even though it was "graduated already). Still, the trees in area "A" are underexposed vs area "B" even though they are int he same light and general exposure range). In some images its worse than others, sometimes it goes un-noticed (well, not really, but it's tolerable and an untrained eye may not even notice). With the digital era I prefer to take two or three seperate exposures (easily achieved with bracketing) and blend them in PS (though obviously you need the camera on a tripod). Many pros started doing this even when they were still shooting film and then scanning the images.
I do not use any colored filters for my images. You may want a 3-5 stop ND filter just to hold back light over the whole scene to blur moving water (forces a longer exposure). Sepia, and all that can be done in PS. Then you have more control over the tones, saturation, and areas it affects. Plus you still have an orginal without manipulation. Anyway, that is just my preference and style.