Europe Trip 2018-Netherlands, Belgium, Austria, Germany, Switzerland

Your post says 2018, if that is accurate then i hope your itin is just a broad outline so u and friends can have fun talks about the trip way ahead.
I would substitute Brugge over Brussels. Still in Belgium but alot more to do and see. Ck it out. It is magical. It is one of the most beautiful places to visit.

So you're thinking of "...cutting Brussels, Belgium entirely, and then either taking a night train from amsterdam to vienna the night 5 to day 6, or fly day 6 to vienna in the AM. I get more time in each city. I personally would miss seeing Brussels. Suggestions? Comments?"

Isn't that night train the one that requires a change of train at 5:00 am in Passau? Even if that appeals to you, I'd expect at least one of you to sleep poorly prior to 5 am, a circumstance that can impact the group's activities after arrival in Vienna.

The Fuessen "castle" of Neuschwanstein is a late 19th-century palace. Hohenschwangau is a palace as well. So while you might want to see these places, I'd suggest that on your way toward Austria, you spend one night - maybe the night you had allocated for Brussels - in the Middle Rhine Valley, where you can see a real castle or two. Marksburg in Braubach (10 train minutes from Koblenz) is a good option - it's a genuine, never-destroyed medieval castle - and Braubach is an adorable town as well. A'dam to Braubach (8:05 - 12:05) puts you there for the 1 pm castle tour in English. Drop bags at your hotel upon arrival and head to the castle. After the tour, take the train to Ruedesheim and catch a KD cruise boat (4:15 pm) north past most of the 40 castles that dot the river between Bingen and and back to Braubach (7:20 pm.)

(https://upload.wikimedia.org/wikipedia/commons/e/e3/Maeuseturm_Burg_Ehrenfels_Bingen_Rhein.jpg

IMO this would be a more enjoyable day than one spent in Brussels.

From Braubach, head to Munich for Sept. 15,16,17, maybe 18. But I suspect 3 nights there, with O'fest crowds and O'fest prices, might be adequate.

With all due respect to your friends, if they haven't traveled to Europe before, they're not in a great position to know what their preferred travel style is. And since you are apparently the one doing the bulk of the planning, I think you get to lay out a proposal. At some point, if the differences are too great, you get to say, "That's fine. We'll be glad to meet up with you in City X and City Y, and you can do your own thing before and after." At least that's what I would say.

Your proposal offers many opportunities for side trips, which should keep your blitz-trip companions occupied. Your stay-put friends can skip Salzburg and go straight from Vienna to Munich, though I personally wouldn't want a full week in either of those cities, and a week in Munich around the time of the Oktoberfest figures to be expensive.

I'd encourage a flight between Brussels (or Amsterdam) and Vienna rather than the night train. First, they are cutting back on night trains with sleeping accommodations, and we don't know what will be available at the time you plan to travel. Second, the 6:24 PM routing I see for a Brussels-Vienna trip next Monday has a 140-minute layover in Wurzburg between 11:41 PM and 2:01 AM. That will be miserable. When I randomly checked Dec. 6th I found a couple of other routings beginning with that 6:24 PM departure. One was markedly better--just a 66-minute layover in Cologne, between 8:15 and 9:21 PM. Still, all concerned should understand that there are 11 stops between Cologne and Vienna. How much sleep will people actually get?

Edited to add: I really, really like Russ's idea. You'll be a hero to your friends if you include that in your itinerary.

I too hope you're going in 2017 and not 2018.
You said you're going with friends and "none" have ever been to Europe before.
Are you going to be traveling with another couple or is there a larger group of you? Traveling with 5 or more presents some challenges. I hope you're really close friends, as 3 weeks is a long time. And since you've been there before, it's a lot of pressure to put on yourself.
I'm a believer in flying open jaw--into one city and out of another. I'm also big on traveling to cities that are relatively close together and to cities that compliment each other. For example, I like trips to Rome, Florence and Venice. Or, Budapest, Vienna and Prague. Or, Munich, Salzburg and Vienna. London, Paris and Barcelona would fit as they have great high speed rail between the cities.
With the advent of budget European airlines, I like traveling through one region and then flying to a completely different place on the way home. Like visiting Italy, and stopping in Portugal on the way home. Or, going to Berlin, Dresden and Prague and stopping in Copenhagen on the way home. I hope you understand what I'm saying.
As far as your itinerary above, it's really a little too aggressive for first time European travelers. It's likely that much of the trip could be somewhat of a blur. Belgium is somewhat out of the way from Amsterdam to Vienna. I agree about flying between those two cities. Switzerland is more difficult to travel through--and very expensive. We find Austria a great substitute as it's cheaper and much easier to travel through. (It's the same mountains.) You might could spend the time you have in Switzerland in Tirol and have time to head down to Venice. You just have so many options.
I first traveled to Europe as a 20 year old college student. If you're 30 somethings and looking for a lively time, Munich, Vienna, Budapest and Prague would be perfect cities for you. Those Grunge Bars of Budapest are hard to beat.
Whatever you choose to do, have a great time. It could be a trip of a lifetime for you all.

I have learned the hard way that travelling with a group is like herding cats, much easier to earn annoyance that praise. Before worrying about the route, work out these challenges in advance. Well in advance.
Nobody will be satisfied with every choice, whether it is restaurant, activity, or mode of transport. Discuss it all now. The most essential point is that the various travellers feel free to go off on their own, with no guilt or jealousy from anybody. In my group, we meet for breakfast and supper and in between we do our own things. If you are sketching out the route, give the others lots of chance to chip in (or back out). And talk now about how joint expenses will be split up. I travel with friends-for-life and we have stayed that way by leaving plenty of stretch in our plans.

The Amsterdam-Vienna night train is one that is cancelled for 2017, loosely replaced by a departure from Dusseldorf.

Your big cities of Amsterdam, Vienna, and Munich have plenty to see and do, so I would stick with the 3+ nights that you have in each of those.

If you are going with friends, none of whom has ever been to Europe, what makes any of their advice better than yours? On that basis I would not rely on such friends for advice.

The night service from Düsseldorf goes to Munich Hbf, where you can transfer to Vienna. Düsseldorf to Munich night train is the one I took, then transferring to Linz.

In 2018 who knows what the night train situation will be. You will not know what the train schedules will be until April 2018. Plan on flying from Brussels/Amsterdam to Vienna. Easyjet has cheap flights from Amsterdam.

You show driving to Luzern, but you will be using trains the rest of the time you are in Switzerland. It is expensive to drop a car in another country, and you will also need to purchase a Swiss vignette sticker for the car. Consider dropping the car in Lindau, then taking the train to Luzern from there. At any rate, it deserves a little number crunching.

You show staying in Lausanne, which is a big city. Montreux or Vevey will be more convenient more visiting Chateau Chillon and Gruyeres. It is easy to get to Geneva airport from there. I assume that is where you are flying home from.

What kind of car are you going to get that will hold at least 5 people and their luggage? You don't say if it is just 5 or could it be 6 people? That means a mini-van. Will one person drive or will it be shared? Can everyone drive a standard or will you shell out extra money for an automatic?

The night trains aren't fun for everyone. Many people get no sleep. You end up at your destination exhausted. Either fly, or break your trip up into smaller portions.

You must go to Russia!