Transportation from Vienna to Venice in October

You can use the German Train site www.bahn.de to look at schedules and routes, but not to purchase tickets. I would not bother looking at your planned day of travel in October, since schedules may not be loaded, however if you look even just a few weeks out, you can see what the typical schedule is, it may change, but not by much. I did a quick check, and was surprised that bus part of the way is an option. It looks to be shorter (about 8 hours vs 11 by train) and is Train to Villach, then Bus into Venice. Train all the way is an option, a few hours longer, and requires changes in Innsbruck and Verona. Reservations may be required on some parts of the trip if a Fast train is used, but you could purchase the day of travel if that works better for you. I doubt the bus requires a reservation.

If you travel by train from Vienna to Villach and by bus from there to Venice, you can book the entire trip on the Austrian Rail site. (The bus is operated by Austrian Rail and reservations are required.) If you book several months in advance, you can get a 2nd class SparSchiene discount fare as low as €29 for the entire trip.

Thanks to both of you. I checked and have a better idea for planning purposes. We will book as early as possible to get the discounted seats at the very good rate.