Europe for a month by train- itinerary thoughts?

Looks like a great trip with no changes necessary.

If you were to make changes, I would start with three questions: What have I not yet seen that I want to see on this trip? What have I seen before that I want to see again? What do I not need to see again?

IMO these will help you decide between Amsterdam and Lucerne/Interlaken.

Thank you for the advice - you are right about that! It's hard to not want to see EVERYTHING! ;-)

There are only two trains on that trip that require reservation in advance: Basel - Paris (coming from Interlaken) and Paris - Brussels. These reservatons may be hard to come by, so you may just buy a ticket for that.

All the others do not require resevations. Eg. from Milano to Luzern you just take the RE to Lugano and a Swiss IC or IR from there. I would suggest you take the IR that goes over the old route.

The Vienna to Budapest train is only 2.5 hours. Done it a few times, but never 1st class. But I just looked and, on the one date in February I checked it was only 9 euro more to go first class. Next time (and I go maybe twice a year) its might be worth it. Thanks for making me look.

Sure, you don't have to book in advance, its not "required" but doing so will give you more seat options and doing so might get your a lower cost. Not sure how often 1st class sells out. Not many 1st class carriages so maybe faster than the rest? No idea really. Not sure why, once you know what your schedule is, you would wait to buy a ticket?

Check the prices with the Hungarian rail site as it's sometimes less than the Austrisn site for the same train; but not aways. Worth a look though. Their MAV phone app for buying, storing and presenting tickets is pretty sweet too. https://jegy.mav.hu/

You might check out itineraries on the Railbookers site and "borrow" some of their ideas. Youtube is also full to the brim with train vlogs.

Have you been to Interlaken before? I was just thinking it might be more exciting to just go all the way into the valley, at least to Lauterbrunnen, but maybe stay up high. Are you looking to hike? Do high mountain trips like Jungfraujoch? Or you can take a boat from Interlaken to Brienz and go to the open air museum. But everything will be outdoorsy.

Have you been to Amsterdam before? There you are obviously looking more at museums and much more of a city visit than anything around Interlaken.

Most of your stops are bigger cities. I found in my travels although I am drawn to the big cities, when I look back, the smaller towns are usually my favorite. You will know yourselves and whether you need more countryside or you prefer the big cities.

Just some things to think about to help you decide between Interlaken and Amsterdam.

Tigerfan is correct about the small town stops. For a stop on the way to Budapest check out Győr and the Archabbey at Pannonhalma. You can have lunch in Győr and see the Archabbey and it will take about 4 hours. The train from Vienna to Budapest goes straight thru Győr so its not really a side trip; but you will need a taxi to the archabbey and back. But you will lose a half day in Budapest so a little less time in Vienna might be in order.

A well thought out plan, however, I will make a few suggestions.

1) Consider visiting Prague, Nuremberg, Munich and Vienna (skip Frankfurt) first, as well as Salzburg on your way to Switzerland.
2) Budapest could be done as well after Vienna, then to Milan and Switzerland.
3) You need more days for cities like Vienna and Paris. Suggest skipping Brussels and departing from Paris.

Your plan is very busy with lots of travel. Yes, you can see a lot of cities for only 2 or three days, but consider doing fewer and spend more time at each.

Way too many 2 night stays for me, but .... .each to their own.
Next I suggest you go to the forum for each stop and get some input. What you get might make you reconsider the length of stay or give you some other ideas. Then finalize it.