Traveling the Netherlands to Germany

You will find that renting a car in one country and returning in another is quite expensive. Check out AutoEurope and put in different parameters to see what costs are in different scenarios. It may or may not be worth that plan to you. Or you may consider dropping off in the Netherlands; taking the train to Germany, and picking up a new car there.

Thank you. Should we prebook hotels or Bed and Breakfasts, or can we just wing it at that time of year? I am not sure how busy it is in September.

I would second KD's suggestion that you drop off your car in Amsterdam and then pick up a new one in Germany. It's not worth the extra cost. And quite frankly, both of those destinations are places where you could easily do without a car. I spent 3 weeks in Germany and 2 1/2 weeks in the Netherlands, and the only time I rented a car was for 4 days in Germany. And that was only because I was staying in a village where my ancestors came from and the train station was 2 1/2 miles out of town.

But some people want cars so there's nothing wrong about that. However, it can get very pricey to rent a car in one country and drop it off in another; hence the suggestion here and above. :-)

There is a usually a fee to drop the car off in a different company, and it might be quite hefty. Europcar is an aggregator. I just ran a search there, and it didn't break out the one-way fee, but the prices seemed quite high. I saw a recent post from someone with some kind of loyalty account with Avis or Hertz or something that either waived or greatly reduced the one-way fee for them. You'd probably save a lot of money by taking a train to the closest German city with a car rental location. That doesn't work if your goal is to see the Dutch countryside, I guess.
If you are comfortable winging it on accommodation, then by all means, wing it. You won't see a lot of Forum folks recommending that, though. If you start out winging it and it's not working, you can always plot a course and start booking ahead. Even booking ahead by one day can eliminate the anxiety of not finding somewhere to stay.
Have a great trip!

Should we prebook hotels or Bed and Breakfasts, or can we just wing it at that time of year? I am not sure how busy it is in September.

I generally prebook pretty far ahead because I don't like surprises, and your chances of getting a good price and location will be better the farther ahead you book. It certainly would not be too early to book now.

Keep in mind that you should either make sure the hotel/B&B is refundable OR make sure you have travel insurance that will cover the cost if you have to cancel. Refundable is definitely easier so I would go with that if possible.

You may want to check whether the places in Germany you plan to visit have an environmental zone, whether you can access them with a car and what is required to enter them by car (and type of car): https://www.bmuv.de/en/topics/mobility/overview-air/emissions-control-sticker-and-low-emission-zone.

Taking the train may be more convenient and less stressful.

September is still a busy travel season, so I would definitely book ahead. You are also coming into Octoberfest at the end of the month, and even if you're not in Munich, some of the smaller towns also have festivities.
I just don't think it's worth it to spend hours of your treasured vacation time looking for upcoming lodging.
Have a great trip!

“Winging it” these days on accommodation reservations is going to cost both money and precious time if you wait until you’re on vacation. The best properties will be booked up by the time of your trip and what is leftover will be more expensive than if you make cancellable reservations now.
A car is of little use in densely--populated Holland. To avoid the exhorbitant international one-way dropoff surcharge, I would take the trains in the Netherlands and, once you’re in Germany, pick up a car in the Ruhr. ( Bochum, Duisburg, Essen. Dortmund etc.). You can drop it off in a different German city at little additional cost.
www.AutoEurope.com
For accommodations, www.Trivago.com

I'm not sure how valuable it is to sleep in post-war, developer-built single-family housing developments. What exactly do you expect from "towns along the way"? For example, we slept (advance reservation) in Arnhem at a soul-less business hotel because it came with parking, and was at the edge of town, making it easy to come and go for the day. We did manage to walk to an "old" square in Arnhem that was a dining-district, more or less. The dinner area in Andernach, Germany was similar, but the town was not exactly "just vacated by Band of Brothers."

While walking around Arnhem, we did run across a building that had a big inscription, in Dutch, saying that it had been the German Occupation administrative office. But I wasn't sure the of the "value" of driving over the THIRD bridge to occupy the original location of The Bridge Too Far!

You might benefit from determining WHY you are renting a car. Is it because you are American, or because you have specific plans that can best be done by car. ".. to Germany" is pretty wide open, and no one can "see Germany" in one week (or two, for that matter..) It sounds like you have not been to Europe before. If that is so, I strongly recommend that you buy (or visit the public library for) our host here, Rick Steves' books on The Netherlands[ and Belgium] might be the title, and Germany. Also look at his free Travel Tips, blue menu top left on a desktop view of this website. You might wish to post again with a tentative list of cities and nights. There is particularly strong knowledge of the Netherland and especially, Germany, on this newsboard.

Our first five trips to Europe, we mostly stayed in big cities and made typically one daytrip a day by rail, if we weren't fully booked in the large city. I mean, you know you don't want a car anywhere you can see Amsterdam from, don't you! A car there is more than a hindrance, it's a nightmare! Even more than Berlin or Cologne or Paris, Amsterdam is really suitable for quick, cheap, unreserved train trips on unreserved, very frequent local trains, to Den Haag, Delft, Leiden, Alkmaar, Utrecht, Amersfoort, and many more. Leiden and Utrecht each can't be "seen in a day". So seven nights in Amsterdam isn't remotely too much. Be sure to book Anne Frank House well in advance or you won't get in. Some museums may need booking, like the biggest art museums.