Hi Rachel,
Garmisch is closer to being about 1:30 minutes from the Italian border.
Just my opinion, but Bolzano and Innsbruck may be a bit redundant, but we did like seeing the "Ice Man" exhibit.
While we really like Sterzing/Vipiteno, I don't know if I'd make a special trip just to see it. It's a pretty small old town. We've been twice, but both times we were passing by and stopped for a couple of hours. Just a "heads up", both times we were there, the shops (not cafes) closed from 12 noon untill 3pm. It is a charming old town though.
Have you been to Mittenwald? It's less than 30 minutes from Garmisch and is one of our favorite places in Bavaria. IMO, it's the quintessential Bavarian village surrounded by mountains.
Perhaps there's a tour to the Italian Dolomites. The Val Gardena is less than 2:30 from Garmisch. The Alps (Dolomites) here are unlike anything you'll see in Bavaria or Austria.
www.val-gardena.com
Another option could be the charming old town of Brixen/Bressanone, our favorite in the Sud Tirol.
www.brixen.org
Hope this helps.
Paul