Belgium, Germany & Switzerland

While staying in Ghent, spend a day in Brugges. Not sure that I would spend four days there.
Six nights in Germany, you can't do justice to places in the Rhine Valley , Rothenburg and Munich in six nights.
You could spend all six nights in the Rhine Valley OR Bavaria, suggest you pick one.

There are Battle of the Bulge tours available, but not sure you have time.

If you do the Rhine Valley, Trier, Cologne, Heidelberg, The lower Moselle valley, the Black Forest (Triberg) and Strasbourg, France.
There is more to see besides the listed places.

Interlaken is great, go up the Youngfrau. Lucerne is a must.

If you pick Bavaria instead of the Rhine Valley, then don't miss Dachau Concentration camp, Munich of course, Salzburg, Austria and Berchtesgaden, Germany. Also, Garmish/Fussen area and the Zugspitze.

I thought I had a general idea of what to do until I started reading the Forums, now my head wants to explode.

Well, it's good that you are giving the forum a second chance and sharing your plans and preferences - the advice you read previously was aimed at others. With some luck, you will get suggestions that focus on the time frame and the routing you have outlined, and what you read HERE should be a better fit for you!

The entry point from Belgium into Germany will likely be AACHEN (west of COLOGNE.) The ideal exit point from Germany for the destination of Bern, Switzerland is BASEL. So rather than trying to see too much of Germany (Rothenburg, Munich, etc.) and spending too much time on the train in too few days, I think a wise strategy for Germany is to focus on what's between the two Rhine River towns of Cologne and Basel. I don't think the German Alps south of Munich, while nice indeed, compare favorably against the Swiss ones, so save your time in the big mountains for Switzerland.

https://en.wikipedia.org/wiki/Rhine_Valley#/media/File:Rhein-Karte2.png

There are many good choices, but based on your stated interests, I'd suggest this:

Cologne is roughly 2.5 train hours from Ghent. Germany's most popular landmark (Cologne Cathedral) and some good museums can be found there. So... you could arrive in Cologne before noon, drop bags at a hotel, and do some sightseeing there. Maybe NS Doc Center should be on your list if you are interested in WW II.

NIght 1: Cologne

The next morning, I'd catch a train south (1-2 hours) to the Upper Middle Rhine Valley between Koblenz and Bingen, the most scenic part of the Rhine River - think medieval castles and vineyards on steep hillsides, river cruising, wineries, hiking on the Rhine Castle Trail and/or the Rheinsteig trail, and small, old-world towns not so different from Rothenburg... Braubach (home of Marksburg Castle, excellent tour) and Bacharach have much to offer. Trains serve both riverbanks and all the towns on each side.

http://www.loreley-info.com/eng/rhein-rhine/walking-hiking.php
http://www.loreley-info.com/eng/rhein-rhine/castles.php

Nights 2&3: in Boppard, a fine riverfront town on the west bank of the Rhine; a free train pass for outings comes with every reservation here.

The next morning (Day 4) you might linger in the area... or you might be ready to move on to Germany's Black Forest, north of Basel and not far from Freiburg.

Freiburg is a good base if you want to stay in a city with all the city trappings; for a small, old-world town, Gengenbach, further north, is a great base town; it's on the scenic Black Forest Railway and very close to the Black Forest Open-air Museum in Gutach, Triberg, Schiltach and other old world towns. And of course it's a hiker's delight. From Gengenbach, a day trip to Strasbourg France is also possible.

Nights 4-6: Gengenbach or Freiburg

Day 7: Head to Switzerland. Did you stay in Gengenbach? Stop in Freiburg on the way to do some sightseeing there (use lockears at Freiburg station, very convenient walk into the old town from there.)

If you actually have MORE time for Germany, there are other nice places between the Upper Middle Rhine Valley and the Black Forest that can be looked into, depending on your interests.

It is hard to add anything to Russ's excellent post. I like his plan a lot, especially since it keeps you in the corridor of Germany that gets you to Switzerland most quickly.

Thank you, thank you. A great combination of what we wanted to do. I may be back to delve into Switzerland a bit more, but I think that I don't have enough time to do more. Susan