I've only once shot northern lights, but here's my thoughts:
There's no need for fast lenses. You need a sturdy tripod and prepare for multi-second exposures. Sure, they wiggle a bit, but not too much for a few seconds. Wide angle is recommended, because I wouldn't say it's too rare for them to cross most of the sky (depending on what latitude you are).
Also, I noted that having a weak IR-filter in front of the sensor is a good thing, because new colors could be included to the aurora borealis. The time I shoot, the lights seemed only green to the eye, but when looking at the images from the camera, I saw some blue and red colors too.