Jul 24, 2016 - 10:04 AM
Welcome to MySwissAlps Gary!
My preferred route, scenery wise, would be Interlaken - Spiez - Brig - Andermatt - Chur - Pontresina - Tirano. This includes the entire Bernina Express route and most of the Glacier Express route. This will take the entire day: at least 10 hours. Of course you can break your trip if you have time. The timetable gives you all further details.
A Swiss Travel Pass seems like a good idea, but to be sure you'll have to list all your activities (transfers, day trips, museums) and do the math as explained here. Additionally, you would need tickets for the French and Italian portions of your trip.