We sailed 10/11-18/03 and loved it. The seas were fairly calm and we were lucky not to be affected by any tropical storms. I think the one thing you need to keep in mind when you plan an October cruise is that you might not get to the planned ports. The ship will steer around or away from any tropical storms so you may end up stopping in different places. We understood this and were up for anything.
As for doing anything special in October, there wasn't anything on our cruise. I think they do some special activities on the Halloween cruise but I"m sure someone else could post more on that.