Dear all, Im looking for suggestions on my family of 3 adults, train route from Zurich to Italy. We have planned to travel the scenic train from Luzern to Interlake separately on another day.

We intend to travel down via the Bernina Express to Tirano. 
1) Do we have to travel to Chur from Zurich to board the Bernina Express ? Is there any other better station besides Chur which saves time and distance from Zurich ? 
2)  From Tirano, Can we visit Lake como? Which train should we take? 
3) For Travelling Italy via train, Could you suggest possible places to visit. We can have about 8-10 days for Italy and 2-4 days for Austria from 1st June. Our Flight back is from Rome (FCO) on 13th June.
4) For Italy, Could we plan a city to have as our base to visit the rest of the places like Venice, Rome, Florence etc. Or we can also stay for 3 days in each of the main cities. We have a daily Eurail global pass valid till 13th June. If there isnt any nice places, we can also go shopping or unique factory visit like BMW,Mercedes car etc. 

Every valuable input is much appreciated. Thank you