Last summer we spent 3 weeks driving this route: Munich to Ortesei to Venice to Strea to Kauterbrunnen to Colmar to Vacgarach to Frankfurt.
My advice:
Have cash in hand for tolls, in case the credit card reader doesn’t work.
When driving on toll roads, you will get a paper ticket at the booth at the start of the toll section. At the end of the toll section, you put that ticket in the machine then pay the amount on the screen. Then it gives you the ticket back. Have your navigator put that ticket away, so you don’t get it confused with the NEXT ticket you get.
Know your credit card pin. We needed it to buy gas at unmanned stations.
Don’t assume the autobahn has no speed limit. (We’ll be receiving a ticket one of these days…)
Speed cameras are everywhere. Obey the speed limit (see above!)
Have a data plan to use navigation on your phone. Also download maps to use offline in case you have no service.
Add some time to whatever Google maps tells you it will take to get from point A to point B.
If you miss your exit on the freeway, it could be 20+km until the next exit.
Roundabouts are everywhere. Get familiar with them if you don’t have them where you live.
Get the zero deductible insurance.
Expect parking to be limited and expect to pay to park. Get familiar with the parking disk system for limited free parking in certain areas. They don’t typically have big shopping centers with giant free parking lots like in the US.