Support with 4 Week Central Europe (Netherlands, Germany, Austria, Czechia, & Poland) Itinerary

You will indeed get different recommendations on how long to stay because everyone has different levels of interest in different things, as well as different travel styles and energy levels. Lol.

First, I think you have reached the right conclusion about not having enough time to add more locations. You have a full schedule and no time for a late morning or day off. Second, remember that with how you have your trip laid out, on the day you change locations, you lose part of the day to travel (how much of it depends on how far you are going, but even with only a 2 hr train ride, it would be @ 4 hrs so all morning - sometimes it will be more). Many museums will close at 5:00.

I don’t know the Netherlands or Germany, so I am joining you in Salzburg.
Austria days are doable. I advise not getting too attached to your day trips, as you don’t have an excess of time and may decide to stay in the city. And as gorgeous as Hallstatt is, you might prefer an equally close historical site. Bratislava only if you are bored with Vienna after a day.

Czechia is doable. People may say stay longer or skip day trips (and I could easily spend longer - but you will get a feel for it in that amount of time. Again, be ready to skip your day trip, unless it sits high on your priority list.

Poland - not so doable. At a fast run, you could take a tour to Auschwitz & Wielicczka Salt Mine on the same day and see Krakow old town on a second day. So….
Take a day from Krakow and give it to Warsaw. It is impossible to see these worthwhile museums there in half a day (which is all you have after getting there). 1 1/2 days is a sprint through. You will probably find you are wishing for an additional day.
TriCities - again questionable. But in this amount of time, you can see Malbork and a couple of the good museums in Gdansk. Probably not further out.

And I leave you in Germany.

You also need to take a close look at when you are where on what day, etc. As an example, often museums are closed on Mondays (but certainly not all everywhere). You would hate to plan this extensive a trip around certain sites on a very tight timeframe - only to get somewhere and it’s closed that day.

You have an exciting trip ahead! Enjoy!!

"I will be leaving March 22nd, and returning April 21st."
Assuming that's next month, I'd make sure you have your ducks in a row with reservations and such to museums. Over in The Netherlands board, you'll see folks (like me) posting about the importance of getting things like the Anne Frank House reservation made as soon as the tickets open up for the day you want.

Review your itinerary and check out each of the sites entry requirements. If you have a FIRM idea for days you will be in certain places, make the reservations because odds are, it is more of a hassle once you are there and spots are full.
For the more specific country by country stuff, head to each country specific area here, and post a question there. I think folks read across categories/countries, but more specific info is usually offered in the country sections.

Wow! It’s good to see that you have done so much research and planning. That makes it much easier for us to help you. I assume you have bought your plane tickets. If not, it would save time and money to fly home from Berlin. Also, you haven’t factored in travel time between destinations, which will shorten your time in each.
Speaking of Berlin, you do know don’t you, that there is very little of the wall left. Three days is hardly enough to do the city justice. I recommend that you get a reservation for the Reichstag tour, if there are any slots available. I think I’m remembering accurately that there is a good museum of German history. I don’t think you have time for any day trips; but, if you lengthen your stay, Potsdam is an obvious choice.
We did visit Czesky Krumlov, and were glad we did. I particularly wanted to see the Egon Schiele Museum. However, as I recall, it is a bit cumbersome to get to, so maybe not to be included in this trip.
You are really shortchanging Vienna. Our first visit was for 5 days, and we went back for a week the very next year. If you extend your time there, Melk, with its medieval monastery, is a good side trip, especially if you do it by boat.
Keep coming back here, and you will get plenty of useful advice.

Much of your trip, you will not spend enough time in the location proposed.

Example, Amsterdam you propose Day 1/2, assuming you arrive at noon and depart the next day, you will have about 24 hours to see this city. We stayed a week last year and it wasn't enough. Assume you book the Anne Frank House and manage to do the canal cruise, you won't have much time to actually see the city and certainly not the Rijksmuseum or Van Gogh Museum, both of which are amazing.

Other plans like Austria, Prague and Krakow look good. Berlin needs more time and why not Munich?
Further, your travel time between places will eat up a lot of your time. Using rail, have you determined you time getting to train station, then taking the train for X number or hours then taxi to hotel, etc.

I congratulate you for doing the research to identify sights of particular importance to you. Our interests don't overlap very much, but I never knowingly pass up a museum or historic site related to WWII or the Cold War. I spend a shocking amount of time in 20th-century historical museums, so I'm not recommending you budget for visits like mine. However, the relative amount of time it took me to read all the English explanatory material and watch English-subtitled videos at key places in the cities you plan to visit may help you estimate how long you'll want to be in each city.

Prague - Museum of Communism: at least 3 hours
Krakow - Auschwitz: at least 5 hours including the bus ride from Krakow.
Warsaw - Warsaw Rising Museum: 8 hours
Warsaw - POLIN: 8 hours
Gdansk - Solidarity Museum: 8 hours (recommended--you need a success story)
Gdansk - World War II museum: 20 hours

Places you need to book ahead of time because they sell out; you may already have a problem--check today!

• Auschwitz. Online tickets sell out considerably in advance. You don't want to have to head out of town on speculation, just to line up (outdoors) for perhaps more than an hour with your fingers crossed.
• Anne Frank House. You're way late on this one.

You didn't mention the Schindler Factory in Gdansk, another popular sight. It sells out ahead of time.

One place for which you may want to buy a ticket ahead of time to avoid a non-trivial ticket line:

• WWII Museum in Gdansk. I waited in line about 15 minutes back in 2018, and more people are traveling this year.

The Warsaw Rising Museum, POLIN and the Solidarity Museum are popular and were very busy in 2018, but I didn't encounter significant ticket lines; that situation may be different today.

In the unlikely event you have more time in Berlin than in Prague and can add a sight, the DDR Museum in Berlin covers some of the same topics as the Museum of Communism in Prague. Either would be worthwhile for a look at what life was like beyond the Iron Curtain.

The hard truth is that you are trying to see an awful lot of major cities, not to mention the sights within them, in just 28 full days, and it appears you're going to be facing inter-city travel on about 14 of those days (maybe more, depending on your day-trip plans). You have serious interests you want to cater to; you aren't just trying to get a look at a few famous buildings you've seen pictures of. Result: You don't really have enough time for all the places you want to see, and I'm afraid you're going to be stressed as you try to figure out how much you can cram into your days. You're going to learn about additional sights in the remaining time before your trip, which is going to make the itinerary squeeze worse.

I urge you to postpone Poland, a geographical outlier that is also huge. Warsaw has a lot more 20th-century-history museums and sights than you can even contemplate visiting on this trip, and there are many attractive and interesting Polish cities and towns not on your itinerary. Poland is worth a lot more time than you're giving it this year. Keep it for a follow-up trip that could include Hungary, a country you're skirting this year. Budapest is a very attractive city, and Hungary has a lot of other worthwhile destinations.

Time freed up by postponing Poland would allow you to spend more days in the remaining cities. Berlin, in particular, has a very large number of historical sights related to WWII and the Cold War--probably even more than Warsaw.

Wartburg Castle is outside of Eisenach and reachable by public bus. I visited it on a day trip while staying in the pretty university town of Erfurt. The city of Weimar is another good side-trip from Erfurt. The Buchenwald concentration camp on the outskirts of Weimar is accessible by public bus. The original Nazi camp was used to imprison enemies of the DDR government after WWII ended.

I would suggest the cities of Bielefeld and Detmold since you'll be in Westphalia anyway. It sounds that history in antiquity is your main focus. Why Bielefeld and Detmold ? Because of the relic sites and excavations connected to the battle in the Teutoburger Wald should you be interested in that. Programs I have seen on this topic connect Bielefeld as closest town to the battlefield site, check with the Tourist Office there.

On Detmold....Unlike Bielefeld I have been here, once in 1984, made it as a day trip from Soest/Westfalen, the oldest city in Westphalia, also a Roman settlement before they pulled back.

In Detmold are 2 sites I would recommend fitting into your interest area....The Hermann statue, (das Hermannsdenkmal due to his leadership in that fateful battle) and in terms of natural history, the Externsteine....quite amazing.

Even though I have traveled in this region, ie Westphalia numerous times, I can't recommend any places to stay. I stayed several years ago in a Pension in Münster/Westf.

You could look into those in Osnabrück or Soest, if you want a smaller town instead of being in a city.

"Love hiking and nature." You certainly are in an appropriate area to do just that...the hiking in the Teutoburger Wald.

Wow!!!........

You may wish to do some climate research, especially for exposed outdoor places like CK and Auschwitz. I see numbers like 40 deg F in March.

Certainly. I was in Rome, Naples and Salerno during the first half of March 2023. The weather was right around the published averages (i.e., quite nice), but it struggled to get up to 40F much before noon. Mornings were distinctly chilly. March isn't a time I'd want to be in Central Europe, but I'm a wimp.

I like Weatherspark for temps. They show averages by time of day and have probability bands for higher and lower. Looks like sweater weather with maybe a light shell most of the time and most places to me.