Rounding out our itinerary AND deciding on nights per town.

Well, Vienna makes for a nice stop between Prague and Budapest. And between Prague and Vienna I would highly recommend Brno in the Czech Republic (it's right on the rail line between the two, thus no back-tracking anywhere).

As to length of time in each place, and assuming you don't want to take day trips out of any location (with the exception of Auschwitz out of Krakow), the minimum I'd spend is 3 full days in Krakow (4 nights), 2 full days in Prague (3 nights), and 2 full days in Budapest (3 nights). I'd allow more time if you wanted to do day trips.

Because the 25th-9th includes travel days, you really only have about 12 full days on the ground in Europe and a lot of ground to cover. I'd be hesitant to add much more to the current itinerary unless it was just an overnight somewhere along the way (like Brno).

I must throw in my two cents for hallstat. It was off the beaten path, but oh my goodness. It's one of the most photo perfect locations I've seen. Lovely little town.

I think you should look at train schedules and figure out how much time it will take you to get to each new destination. Take into consideration that you will be jetlagged when you arrive and maybe wiped out after that long-haul flight. You probably wont be up to very much on your first day. I think you will find that you don't have as much time for sightseeing as it looks like on the calendar.

Vienna is on the train route between Prague and Budapest and I loved it but 2 days is scratching the surface there.

How long you "should" spend in each place depends a lot on your personal travel style and your interests.

I agree that you might just want to stick to the cities you've listed and consider some daytrips to round out the itinerary. From Prague, you can go to Cesky Krumlov, Kutna Hora (or both). In Budapest, we spent most of a day wandering the the Roman ruins at Aquincum and almost another full day in the Szechenyi Baths. Though they're not really out of town experiences, they are both time-consuming. From my experience (and we did the same basic trip in 2009), I'd suggest five nights Budapest, three Krakow, five Prague and one Cesky Krumlov. However, just a note: I love Prague, while some people on this board adamantly do not, so that's definitely a judgment call on your part. If you're just seeing the sights, you could make it on a minimum of three there, I guess -- I just love exploring the city.

You should undoubtedly visit Istanbul. Great city where you can spend 3 or 4 days of your vacation. Except for the numerous mosques, museums and churches, don't forget to visit Tria Elegance restaurant at Tria Hotel - nice place for a romantic evening to fix in memory this magical city!

Michael,
We flew into Warsaw last April to make easier connections. Spent 2 nights and loved the city. Lots of history. Lots of reminders of the plane tragedy in both Warsaw and Krakow. Took the train to Krakow etc. You'll enjoy all those cities!

I agree that you're pushing it adding anything else onto your itinerary. Remember that a lot of time gets eaten up traveling from place to place, whether you go by train or car. The more places you add into your itinerary, the more time you spend traveling.

I would stick with the 3 cities above, and take a few day trips as suggested, such as to Cesky Krumlov. I would also suggest buying an open-jaw ticket so that you fly into one city and out of another (which you may have already thought of).