Need help with Austria/Northern Italy Intinerary

Last fall we took the Rick Steves My Way Alpine Tour for the purposes of hiking. We stayed in Salzburg and recommend it; interesting historical sites, great restaurants, easy to navigate, and beautiful vistas. I also recommend Castelrotto in Italy (not too far from Innsbruck). From there it is easy to get to Alpe de Suisi which is an awesome place to hike. The hiking is not too strenuous (unless you want it to be), and the meadow goes on and on with a different view around every corner. It was a highlight of the trip. We also liked Innsbruck as easy to get to and easy to navigate. Just a short walk from our hotel we were at the funicular that took us up the mountain for excellent hiking, great "huts" for food and beverage, and awesome views. While there might be small towns near by, we found Innsbruck to be very convenient and interesting.

I enjoyed a week in the Alta Pusteria/Pustertal area in Sexton/Sesto with views of the Three Peaks (South Tyrol Dolomites UNESCO World Heritage). Good hiking in this area too. I do not recall train access to Sexton/Sesto. Off season many places are closed so May may be a little early. Unique in this area are the bunkers dug into the mountains during WWI. Sexton/Sesto was shelled during the war too.

http://www.drei-zinnen.info/en/sesto.html

A couple of suggestions:
Halstatt, near Salzburg. Pretty little town on a lake. Can be reached by train or car. Has salt mine tour near by, Entry area to salt mine is reached by funicular and has a great view of the town and lake.

San Gimignano, 30 miles or so from Florence. I would choose Florence over Milan, unless you have a goal of seeing Leonardo's "Last Supper". San Gimignano is sometimes called the Medieval Manhattan. It was built in an era when mine is bigger than yours ruled.

Your itinerary is too ambitious. You want to visit six cities in 18 days. Considering that you need half a day at least for arrival and departure, as well as for a transfer from one city to next one, you end up with 13 to 14 days net time, i.e. slightly more than two days per city. Should you consider additional day trips - like Hallstatt from Salzburg - the time is even shorter.

For me, a vacation should be somewhat relaxing, not stressful following a tight schedule. In Austria there is a saying: The Austrians work to live, the Americans live to work. Compared to the US everything is slower in Austria, and this is incorporated in the mentality of the people. I think that is somewhat appealing. Unbelievable for most Americans is the fact that in Austria the minimum annual leave is five weeks by law for employees. So the Austrians have much more time for vacation, and need not to hurry.