Munich and Vienna each need more than just a day to visit. If you plan to travel on the morning and return on the same day, then you are wasting a lot of your time. Innsbruck-Munich non-stop train service takes nearly 3 hours, and Innsbruck-Vienne non-stop train service takes about 5 hours. Add on the return journey, you do the maths. You'll be on the train more than you'll be in those cities.
Innsbruck-Bolzano takes about 2 hours to travel on non-stop train service, and you could do a comfortable day trip for that, since it takes less time to travel to Bolzano plus it is a much smaller town compare to the cities of Munich and Vienna.
1. I don't think there is a need for a rail pass. If you buy one, you will need a rail pass for 3 countries - Austria, Germany and Italy, and it's hardly worth your while spending over €300 for that. You're better off buying tickets as required.
I just had a quick look at OBB (Austrian Rail) website and did a quick search. Innsbruck-Munich one way costs as low as €19 (2nd class, adult, normal rate, non-stop train). Innsbruck-Vienna is more expensive, with one way ticket at €58.30 (2nd class, adult, normal rate, non-stop fast train) although if you don't mind adding on another hour of travelling time and a couple of train changes, one way ticket can be as low as €29. I can't seem to get a price for Innsbruck-Bolzano on OBB but Trenitalia indicates the ticket to be as low as €15 one way (2nd class, adult, normal rate).
2. I have not been to Bolzano at this time of year but looking at your rough itinerary right now, it looks like a much better day trip than the others. You'll be hard push to find somewhere else in Italy to visit if you're constraining the travelling time to 2-2.5 hours of train travel, considering Bolzano is already taking 2 hours as it is.
(ps: I did the train searches very quickly based on a random day two weeks from now)
[ Edit: Edited on 02-Nov-2009, at 00:46 by lil_lil ]