October is a little quieter and it should be possible to find accommodation on arrival. My recollection is that a number of international travellers had found their way there via Munich and the Octoberfest. The weather is likely to be better in October but having been there on another occasion during a quite spectacular electric storm I really wouldn't worry about the weather too much.
One point, If your budget stretches to it and you arrive from the airport, Get a water taxi into the City, Its quite spectacular day or night. Not cheap but much better value than an overpriced Gondola ride.


