believe me one will be enough. and the ride from salzburg to innsbruch on the train is probably 2hrs+ the train goes back half the way to Munich and then turns into the Inn-Valley. Salzburg also has way more to offer than Innsbruck does.

There will be almost no tourists in November. So Salzburg deffenitly is the better choice.

On the other hand if you want to rent a nice car and do the alpineroads i can understand that as well ^ - but i would wait and see what the weather is like. in the rain it's no fun either...