Salzburg, Vienna and Prague

You note that you will have 2 1/2 days in Vienna and Prague. Is that 2 1/2 days in each, or both? If it is total, does the 2 1/2 days take into account the travel time between Vienna and Prague? If you have that much time in each, you can do it fine. If that is the total time for the 2 and travel time comes out of that 2 1/2 days, you should skip one place or the other as you will fine one day in each as of little remembrance. I have been to both Vienna and Prague and would recommend as much time in each as you can manage.
Happy Travels

Definitely take the SOM tour in Salzburg. Super fun and efficient. It will take much longer on your own, and some of the locations are not as recognizable as you might think.
Vienna needs at least 2.5 days! Hofburg Palace, including the treasury, Stephansdom, the Kunsthistorisches (art) museum are just a start. For the money, I'd rather go to the opera than the Spanish Riding School. You can view a practice at the riding school during the day that is cheaper, but the show is not as fancy. I think the Vienna Boys Choir is better seem somewhere besides Vienna--they are hidden in the church balcony, so you can't see them. Sounds beautiful, though!

We do have two and half days in each place. That does not include any travel time. We are actually spending three days in each but I am saying 2.5 considering travel time. How do I find out the practice times for the Spanish riding school? Is there a particular SOM tour we should take? Is this something that needs to be booked in advance?

I enjoyed Bob's SOM tour. They use vans while some of the other tours use bigger buses. I would suggest reserving in advance. If you are really familiar with the movie, you will find some additional sites in the old town that you can walk to, and that the tour will not visit.

I just googled Spanish Riding school Vienna http://www.viennaticketonline.com/spanish-riding-school We were taken there for a practice session by friends who were then living in Vienna so did not book it ourselves. To each their own but of all the wonderful things we did in a short trip (4 days) to Vienna, this would be at the very bottom of the list. The first 30 mins was interesting enough but they then continue to do the same things over and over....to the same music. It became boring (to us) very quickly. It is extremely popular - this was mid winter - and very crowded so I do think you need to book in advance.

Bob's and Panorama tours both do a Sound of Music tour. We've done Panorama and they were fine. We know people who have done Bob's and liked it as well.

The SOM tours visit the places outside the Old Town area. When I first took one in 1970, it also visited the in town sites but not the wedding church in Mondsee. I remember seeing somewhere on the internet a list of movie locations in the old town. See if you can find that and do it in addition to the organized tour.

I 2nd the Vienna recommendations by Angela other than I haven't been to their art museum. I'd also like to add Schonnburg Palace to the Vienna list. I loved the Lipizzaner Stallions but it did get repetitive so I think a rehearsal would be fine. In Prague: The castle is a must especially for St. Vitus Cathedral; Charles Bridge with all the statues; Old Town Square area with lots of sights including the Astronomical Clock. A lot of Prague's charm is just strolling the "Old Town" and "Lesser Town" areas.

If you're at all into history, be sure and check out the Hapsburg tomb in Vienna. It seems to be largely overlooked by a lot of tourists, but it has the tomb of famous and beloved Empress "Sisi" (cousin to "Mad" King Ludwig of Bavaria) and Franz Joseph. Really cool. I enjoyed watching part of an opera for free outside the opera house. The opera house tour is fantastic and inexpensive. If you want to be able to understand the opera (via subtitles) you will have to purchase a ticket, but the standing room tickets are reasonable (although standing for 3+ hours sounds terrible - I'm just going to splurge for an actual seat next time) The main art museum in Vienna mentioned above is WELL worth a visit. In addition to the main Cathederal, don't neglect the other churches in the center of town if you're into relics. The Opus Dei church (I forget the name of it, but I'm sure you can google it) has a couple full body relics, really creepy and cool. I enjoyed the small Roman ruins/museum as well. There's so much to do in Vienna, you'll have to pick and choose for only 2.5 days but I really enjoyed all that I listed above. Also don't forget to check out a wine bar, Austrian wine is fantastic and doesn't get a lot of press in the U.S.