Combining Glacier and Bernina Express Trains

Glacier Express from Zurich or Zermatt to St. Moritz (2 nights in St.
Moritz)

Not sure why you have "Zurich or Zermatt". Glacier Express goes from Zermatt, so what does Zurich have to do with this?

Most here would suggest nearby Pontresina rather than St Moritz. Otherwise looks fine to me.

I thought there was an option of starting the Glacier Express from Zurich, but obviously not!

Why Pontresina? (I will look it up -- appreciate the suggestion but don't know anything about it!)

Most people advise staying in Pontresina instead of St. Moritz. Lots more charm, less glitz. Youncan start the Bernina Express in Pontresina, it is only 15 minutes or so from St. Moritz.

Pontresina to Verona in one day would be a very long day. Youncould take a night from Verona and stop overnight in lovely Varenna on Lake Como.

Hereis a map of the Swiss train system to help you see what you will be doing.

https://cdn-doc.myswissalps.com/docs/default-source/rail-network-maps/swisstravelpass.pdf?sfvrsn=7788603a_56

Baden-Baden to Zermatt, to St Moritz, to Verona, then Venice is a long time spent on trains. Scenic as these rides are, you might get bored after a while...
Given the choice, I'd focus on the Albula and Bernina railways without going to Zermatt. You'd still travel about 25% of the Glacier Express route if you do so.

That means going from Baden-Baden towards Zürich (or Luzern if you want to visit Luzern), then onwards to the St Moritz area via Chur (to travel the Albula railway), then to Italy with the Bernina railway.

By the way, St Moritz/ Pontresina to Verona via the Bernina railway takes about 7 hours, so it is long but very doable in a day.

It can take a little longer than 7 hours if you want to take the actual Bernina Express panoramic trains, generally because of the way the train changes work. However there are regular trains that run hourly on the same route going past the same scenery, with some better connecting times on to Verona. Note that until about September 10, there is replacement bus service between Tirano and Colico, while they repair the rail line.

thank you all so much!

Balso: can you explain the route from Chur to Verona, including the Bernina Railway? Looks like a couple of changes would be required, right?

Yes!
From Chur to Verona, you always have to change trains in Tirano (border station) and in Milan Centrale. And if you do not take the special, reservation-required Bernina Express, you also need to change trains in St. Moritz between Chur and Tirano.
Last but not least, there is indeed a bus to replace the train until Sep 10 between Tirano and Colico, as Sam stated above. This is timed to meet trains, and probably does not take longer (the train is slow!).

Biggest factor in the train change in Tirano is that the RhB tracks from Switzerland are meter gauge tracks and the Trenord tracks to Milan are standard gauge tracks. Also you have to change stations, but it is a short walk across a piazza between the two stations. The replacement bus to Colico will be in front of the Trenord station.

At Milan, you change trains at Milano Centrale, a huge urban railroad terminal with many tracks and trains going to many destinations throughout Italy. Everything is on one level, so no stairs to contend with if you have a roller suitcase. You have the option of taking a high-speed Freccia (Arrow) train to Verona which makes limited stops, or a Regionale Veloce (fast regional train) that makes more stops, but is not a whole lot slower than the Freccia trains. Freccia trains are more expensive if bought spur of the moment, but can be discounted if you buy a nonrefundable, train-specific ticket in advance. The Regionale Veloce trains are always the same price, which is cheaper than the walk-up price of the Freccia trains. The trains are less luxurious and there are no reserved seats. The Freccia trains come with a seat reservation with the ticket.