The most important thing to factor into your itns is WEATHER. The Swiss trains are punctual and frequent, so interchanging days/trips if bad weather occurs should be considered.
I vote for the FULL GP route: Montreux to Zweisimmen to Interlaken Ost to Luzern. A few of the trains on the M-Z section have VIP seats (extra price and a reservation is required) but the motorman sits above the front seats and you see the (spectacular scenery!) up front.
The boat* from Luzern to Vitznau to take the Cog Railway to Rigi Kulm, but return via Arth-Goldau; take (non-tunnel) route south to Goschenen spiraling around the (famous!) Wassen Church is nice, especially if you just observed the model railway of
that route in the Transport Museum in Luzern.
Zermat as well as Interlaken are super touristy, but the scenery in Zermat is worth a day.
Don't try to do too much, jet lag + general city exploring can be exhausting. Assuming you will return to Switz. in the future, if you have good weather make the most of it, you can always see "indoor stuff" when its raining.
*The boat from Luzern makes a stop at the Transport Museum on the way to Vitznau.
Have a spectacular trip.
Thanks for the response [MENTION=22858]nrr[/MENTION] !
For sure we will be watching the weather closely before venturing up for any of the mountain adventures, and hopefully having the few extra days in Zermatt and Lucerne will help us out in regard to that. Any weather app or website you recommend?
By the way there was a typo between my base 2/3 routes (now corrected), but I see you prefer the later option to get the most out of the GP route. So Base 1 would be Zermatt and Base 2: Montreux, Base 3: Lucern. 2 to 3 via full GP route.
I'll also look into the VIP seat option on those GP sections as well... How soon ahead of the trip would that be available to me? Would I be reserving a seat at the same time as my full STP purchase?
And thanks for the Lake Lucerne tips/trips as well... Rigi over Pilatus in your opinion? Worth doing both if time allows?