Lucerne--Bernina Express--Venice

Yes, this is possible. From Tirano you take an Italian Railways train to Milan, then another to Venice.
This is a long way round, you can get a train direct from Luzern to Milan in less than half the time, but it is very scenic.

You can look up Italian train times and prices on the trenitalia website: http://www.trenitalia.com/tcom-en
Tirano to Milan is a Regional train, no discount for advance purchase and no reservations. Milan to Venice is a high speed train, big discounts for advance purchase.

You would need an early start, as the last train that will connect to the Bernina Express in Chur leaves Luzern at 6:10. This train goes to Zurich and you change there, but it is all on the same level from track 6 to track 5. Same at Chur where you should be able to just cross the platform from track 9 to track 10. At Tirano you actually change stations, but they are across the piazza from each other. Looks like you would arrive in Tirano at 12:45 and there is a train going to Milan at 1:08 pm.

The obvious spot to spend a couple of days on the way is in Varenna on Lake Como, a pleasant resort town with frequent ferry service to Bellagio just across an arm of the lake, and to other spots on the lake. The only catch is that it is downhill from the train station (Varenna-Esino is the station name). Not a big deal arriving, but a slog with a big suitcase when you leave. I suppose there are taxis which could boost you up the hill. Also, there are no ticket facilities at Varenna-Esino station, so you would either need to buy the ticket beforehand for your departure date in Tirano, or at a travel agency or "tabacci" in Varenna. Trains to Milan are at least every 2 hours and it is just a 1 hour train ride. Don't forget to validate your ticket before boarding the Regionale trains. The train from Milan to Venice has reserved seats, so no worries there. Again, tracks are all on the same level at Milano Centrale staion.

Many thanks for these 2 perspectives--very helpful! Seems like the BE option, while doable, has a lot of moving parts. Perhaps I'll just enjoy an extra day or so in Lucerne, then travel direct to Milan and on to Venice.

moving parts, yes, but that's what the Swiss do best - the railways run like a Swiss watch.

I think the original route is doable, especially with three days to complete it. But instead of an early departure to try to catch the official Bernina Express with reserved panorama car, consider taking regional trains along the same route, with the same view. I was happy with that in the past and every connection did, indeed, go like clockwork on a day when I made 6 connections between Varenna and Appenzell. It was so easy to just get on the next, waiting train that I never got around to breaking for lunch. (You can carry your own food and beverage aboard.)

You can depart Luzern at 8:35 or 9:35 for a route via Chur and arrive to Tirano in 7.5 hours with 3 changes or 6.5 hours with 4 changes. But you might prefer to spend a night around Pontresina, Samedan, or St. Moritz rather than staying in ho-hum Tirano or continuing another 1.5 hours to Varenna on the same day. Pontresina-Varenna would take 3.5-4 hours on another day.

How much do you like tunnels? The direct route from Luzern toward Milan uses the new Gotthard Basistunnel, one of the longest tunnels and n Europe ( or maybe the longest--I did not check). You go under the Alps and do not see them.

The route Laura suggested does not have all that many "moving parts", expectially if you use a regional train on the Bernina Pass route instead of the designated Bernina Express. We did exactly as she suggests when we went to Venice two years ago---purposely flew into Zurich to ride the Bernina Pass route. We went as far as Samedan the first day, and spent two nights there to have a full day to hike. But you could spend just one night in the area---lots of choices, including lovely mountain inns.

Then continue Onnthe route to Tirano, changing trains there for the ride to Varenna. You can take a taxi to you lodging for the night if luggage is a problem. Hotel Olivedo might work well, as Albergo Milano has steps no matter which way you approach.

From Varenna is is an easy 1-hour train ride to Milan, where you catch the fast train to Venice.

An alternate suggestion from Luzern would be the Gotthard Panorama Express:

https://www.sbb.ch/en/leisure-holidays/travel-in-switzerland/panorama-trips/travelling-gotthard-panorama-express.html

Boat from Luzern to Flüelen, train from there to Bellinzona, with some short tunnels but still views of the Alps. From Bellinzona you could easily catch a train to Milan and on to Venice. Or there may be a shortcut---I did not check the route.

I can't thank you all enough for your responses! Knowing that I can do the equivalent of the BE on regional trains without the same time constraints ...that's a plus. Honestly, my ultimate dream is to sort of "wing it"--not having firm reservations for transportation and lodging but figuring it out as I go, knowing I have a set destination and arrival time I have to work within. Sounds scary right now, but obviously lots of people figure it out, and with practice I ought to be able to use these great train systems, right?

Correct. The advantage of regional trains in Switzerland is that you can just "wing it" if you like. We rarely travel with train reservations in Switzerland.

We recently did this, but in reverse order. We left Milan in the morning and ended our day in Zurich that evening. Since we viewed this as a "one time" thing, we opted for the dedicated Bernina Express and first class.

It was well worth it in both cases. We loved the bigger windows and more space of first class.
However, that's a personal choice. The scenery is the same if you take the "regular" train - but again, we loved the experience.

If you opt for the dedicated train, it clearly says which that is on the schedule. We also opted to make an earlier train from Milan to Tirano because we wanted some time in between trains. Going from Chur to Zurich, we just took the first connection. .

You might want to spend the night in Milan before heading to Venice -or you can just continue on.
Either way, it's a wonderful journey.

These great answers just keep on coming... With each one I think I'm getting clearer on my priorities and time planning, so thanks All! I actually fly into Munich, where I'll spend 3 days and was then going to Lucerne from there as I've heard of its beauty and charm. I'm now contemplating passing up Lucerne for (hopefully) another trip, and instead taking the train from Munich to Chur, as to avoid that early departure from Lucerne through Zurich and on to Chur to catch the BE. Does anyone know if Munich to Chur is a beast of a journey, i.e. tons of connections? If fairly easy, I could stay in Chur the night before, easily make the BE next am and get it out of my system!😊 Would Tirano on to Milan (after disembarking BE) in the same day be reasonable? Many thx--

Does anyone know if Munich to Chur is a beast of a journey, i.e. tons of connections?

You can easily look this up yourself, on the DB (German Railways) site (hasn't anybody told you this already?): https://www.bahn.com/en/view/index.shtml
Just enter from: Munich, to: Chur, date and time and it will give you all the trains, with connections and stops.

Would Tirano on to Milan (after disembarking BE) in the same day be reasonable?

Yes, same answer, look it up on https://www.bahn.com/en/view/index.shtml
This site is good for trains for all the main rail companies anywhere in Europe.
I was surprised you didn't know there were other trains on the Bernina Pass route. Every rail line and every station in Switzerland has at least one train per hour in each direction. the Bernina Express is an extra train on the route with panoramic windows for tourists.

Yes Chris, I am aware of all you so generously pointed out. Train tables can a bit intimidating and confusing to those of us who are novices.

don't forget to check out that guy in seat 61 for train info