Is it bad form to have a different number of audio tracks from video tracks?
I always avoid excess tracks.  You can add as many or few tracks of each types as you want in "Add Tracks..." Simply adjust the number of tracks to be added by clicking on the number.  It defaults to 1 video and 1 audio track, but that can easily be changed each time you add tracks.  

You can also add an individual track to either by right clicking in the header area and saying Add Track.

As far as industry standards go, I've never heard of a standard and I've never known anyone to think anything of having unused tracks, but cleanliness is always a plus.  There is certainly no standard to intentionally use excess tracks, but in my experience nobody is going to think anything if there are a few excess tracks either.  Generally cleaning up after yourself does look a little more professional though.