Hi Julie, welcome to MySwissAlps and greetings from another Canadian!
I think, based on your list above, the best towns for you to stay in are Luzern, Interlaken (or if you would prefer a smaller "alpine" village: Lauterbrunnen, Wengen or Murren) and then Montreux.
Have a read through those town pages I linked and of course the regions of Switzerland, to see what appeals to you.
If you are looking for more details on the attractions/points of interest you mentioned, you can find them listed here.
I'm not sure I would try and do the RheinFall and Mt. Rigi on the same day (especially one where you just flew in). Attempting Mt.Rigi if you don't arrive in downtown Zurich until 10 or 11am might be a stretch as well but possible on a long day if you are up for it. The RheinFall would be fairly simple to do however.
I'm not sure I can recommend any mountain that may be less cloudy than another. Our usual recommendation is to wait until the day before to decide what mountain, if any, to go up the next day (based on the weather).
Luzern, Bern and Montreux are some of my favourite towns in Switzerland; so they are good options if you don't go up a mountain one day. A train trip on the Golden Pass Panoramic train from Luzern to Montreux is a great trip.
As for the two cities you mentioned above: Mulan and Curr..I think you meant Milan and Chur? I am not too intersted in Chur, I think stay there only if needed for the Bernina Express train departure time.
I am not sure any one town is more expensive then another (Switzerland is very expensive) but Zermatt and St. Moritz stand out as very expensive towns in a very expensive country.
When looking through our information pages on towns, there will be a tab for "hotels" you can click and search through our recommended options - for each budget type.
Lastly, I think the Swiss Travel Pass would indeed be your best option. You can read more about it and buy it online here. It is then emailed to you to be printed out before leaving home. That way you have an electronic back-up and you can just jump on any train as soon as you land - no need to buy any more tickets (except one a few routes listed here).
I hope that helps get you started. As you have more questions don't hesitate to ask!