Rail stopover choice & is Meirigen logical as a stop?

Meiringen (note spelling) is a nice little town BUT.
I am assuming your actual route is: Lugano - Luzern (local spelling) - via Brünig Railway - Interlaken - Spiez - via Golden Pass route - Montreux. Meiringen is one of the many stops on the Brünig Railway, It is nothing (for the Swiss Alps) exceptional.
Option 1 : Stop at Brienz (on the lake of the same name).
Option 2: (my recommendation) at Interlaken, Take a side route into the Alps, stay at Grindelwald, Lauterbrunnen or Mürren for 2 nights. Then back to Interlaken to continue your trip.

Chamonix --> St Moritz --> Tirano --> Lugano --> Lucerne / Luzern is a long circular route. Have you timed this out? Can it be done in one day? See http://sbb.ch

I plan/hope to do, Chamonix via Mont Blan Exp>Montigny then Glacier Exp>St Moritz>then stop. Next day is thought to be St Moritz >Tirano via Bernina Exp then Swiss bus to Tirano then N to Lugano for another stop. Next travel day would be Lugano>Luzern via William Tell Exp.. Then, as was suggested earlier by Sam from Green Bay, from Luzern to Montreux (via Meieringen as a more scenic route) then stop. Next travel day will be into Paris from Montreux.
Ideas are sure welcome!

At this point we have zero lodging and only air tics & rental car purchased.
Related question: Do I buy the Swiss pass from web?USA now?
Seat reservations for Glacier Exp. are required-do that when?
Other trains & one bus done in country buying a ticket and seat reservation at point of departure?

I'd say take a 2 day break in Luzern. This is a popular city, you can take excursions on the lake, ride on the one of the mountain railways to the top for great views if the weather is clear.
Your route involves 10 hours on the train for the first leg from Chamonix to St Moritz with an early start. Second leg is 6 hours, note it is Bernina Express to Tirano followed by a bus to Lugano and there is only one such connection every day leaving St Moritz around 11 am. Note the bus is really nearly due west. The third leg is the shortest, only 2 1/2 hours to Luzern. You can leave early afternoon after exploring Lugano in the morning. The last leg is 5 1/2 hours with changes in Interlaken, Zweisimmenen (if you get the right train) and Lausanne. From Lausanne get an advance purchase nonrefundable Prems fare from www.capitainetrain.com for the TGV Lyria straight to Paris.
The 3-day Swiss Saver Flexi Pass for 234 chf, It acts as a Half Fare Card on the days between the first and last day of use. You can buy leg 3 for 29 chf, that way saving about 21 chf over getting a 4-day flexi pass. It will also give you half fare on local transit and excurions in Luzern or wherever else you take a day off.
You can buy in advance from the RS, or from www.sbb.ch, or buy when you are there. The reservation fee for the Glacier Express is 33 chf, and 14 chf for the Bernina Express. You can buy them when you are there. I doubt the trains will be sold out in September weekdays, but you can reserve in advance for peace of mind.