Ideas for first trip

Our favorite time to travel is mid April to Mid May. All of the sights and shops are open that time, however a few mountain passes might still be snowed in.
I wouldn't worry about Oberammergau one bit. It's southwest of Munich where Rothenburg is northwest of Munich a distance. There are so many other Bavarian towns that you could substitute in lieu of Rothenburg too.
Let me warn you that the distances in both Germany and France can be deceiving. These are both large countries, and you don't want to spend all your time driving.
We used to drive mega miles on our whirlwind trips to Europe, but the high cost of gasoline (in Italy) slowed us down greatly. One of our favorite trips was to fly into Munich, visit the city for 4 days (including Dachau) and head southwest through Bavaria down into Western Tirol. Then turn east toward Innsbruck and north to Salzburg. From there, it's a great drive east to Vienna or to Linz and north through Cesky Krumlov to Prague. The trick is getting back to the originating country where you picked up the rental car to avoid huge drop off fees. Anyway it goes, we're in love with The Alps.

Just add to Davids post- having a rental car is a great asset for the portions of your trip where you may be exploring primarily rural areas or small villages not served by trains. BUT a car can be a huge headache in cities, where traffic is dense, parking is scarce and expensive, and there are an abundance of narrow one way or pedestrian only streets. Also, if you rent a car in one country but drop it off in another, be prepared for a huge ( and I mean HUGE) drop off fee. Not to say you shouldn't rent a car when you need one, but if you can easily get from A to B by train, then do it. And use public transit while in the cities.
Your planned trip looks ambitious for only a 2 week trip. When planning, take careful consideration of the travel time to get from place to place, and adjust things (perhaps even eliminating places) so that you'll have enough time to see what you want to see in any one place before moving on. Unless you only want to see the passing scenery out the window as you speed by, that is.

Make a list of the cities and towns that interest you. Then make a list of what it is you want to see and do in each of these places. This, plus the estimated travel times you can get either from viaMichelin or Google Maps will help you see how you're doing for time, how many days you need in each place, and where you may need to cut.

Hello Cheri,

Your initial itinerary thought is quite ambitious. I would pick one country and go from there.
I spent a month in France and a month in Germany. I found France to be the most enjoyable by car. I covered the Loire Valley, Dordogne Valley and Provence. I realize you only have 2 weeks so I would suggest Dordogne and Provence. Germany is a very large country and although have some great places to visit, the major cities are spread far and wide and I didn't drive. I used trains because as stated before, cars are a pain in large cities. I would vote for France, but only you can make that decision. Once you narrow it down, I think you will get more help here on the forum. Good luck on your planning.

Bavarian tourism numbers are highest in summer (see monthly overview on page 3 of embedded pdf at bottom of linked webpage). So April / May is somehow mid-season - it would not be filled maximum but you will still find a lot of tourists especially at and around the hotspots.

Most important tip: Do not plan your trip with too large distances and with too little time at a place.

Be aware that May 1 is a national holiday on which shops has closed. As well shops are closed on Sundays in Germany. In Bavaria try to be at a place with Maypole event.

One of the best pages to plan your trip is provided by German National Tourist Board. Use the map and add interests by click to get the most interesting sights at places you like to visit. Also Bavaria tourist website is very helpful.

Some tips for trip to / in Germany. I suggest to have also some cash in coins with you (e.g. for visiting public toilets). In a lot of traveler use cases smartphone based payment solutions bring you much in Germany, e.g. luggage lockers.

Personally I suggest to avoid Google Maps. Here WeGo and Sygic have better and more accurate map material. Sgic has a fully offline map - no need to care for loading special offline areas left / right.

Last tip: Prepare yourself that the real Germany - even Bavaria - will be totally different to the Germany version that you will find in German belt of Texas, e.g. Fredericksburg or Boerne.

Do you 2 weeks include any time in Paris?
If not, in 2 weeks, it is just about reasonable to drive a sort of inverted C-shape route from Strasbourg/Alsace to Heidelberg, Rothenburg, then Bavaria, then back west to Burgundy / Dijon by way of the Black Forest.
Anything longer - south to Lyon, north to Belgium - sounds like a stretch.

Our first trip was also to France & Germany (with a little Austria thrown in for good measure since it's right there!).

Fly into Paris, out of Munich.

4 nights in Paris - then TGV to Frankfurt and pick up car.
2 nights in RodT
2 nights in Fussen
2 nights in Hall in Tyrol
2 nights in Salzburg
2 nights in Munich

Easy driving from location to location... between 1:30 and 2:30

Thanks to everyone for your ideas. I’m taking it all in. And whatever anyone wants to add. At this point in my planning, I could go anywhere! Trying to nail it down soon. MarkK, it sounds like you may be very familiar with our German belt here in Texas. My favorite part of my State.

The general consensus, I can tell, is that we are trying to fit too much in. I will definitely take that under advisement. But I truly don’t mind one or maybe even two longer driving days. We routinely drive long distances here at home. We enjoy the journey as much as the destination.

Two weeks can go quickly with your list. Suggest skipping Brussels.

Explore the Romantic Road, there is lots more than Rothenburg ob der Tauber.
https://www.romanticroadgermany.com
It runs from Wurzburg to Garmisch/Fussen with lots to see.

Lyon, Dijon are great if you want to do Provence and South of France, but that would take much time.
Consider Strasbourg, France and Alsace.