I have an opinion on how to dress and will probably get attacked for it. I always try to wear slacks, leather shoes, and a nice shirt when in any European city port. If you look around you in just about every port, men are wearing sport coats and suits. Americans walking around in shorts and tennis shoes stand out like a sore thumb. Just my opinion.
October is an excellent month to do the itinerary that you are on. Many of the ports can be found in EuropePortReviews.com so you can find tons of info there on what to do and see.