Autobahn does not mean unrestricted speed everywhere. Posted, temporary and electronic limits apply, and traffic, weather and roadworks can require a much slower pace. Keep safe spacing and do not plan a route around high-speed driving.
Some cities retain environmental zones requiring an appropriate emissions sticker. Other cities have removed their zones, so check the current municipal rules and the rental vehicle’s eligibility rather than relying on an old list.
For a relaxed journey, choose fewer overnight bases and leave room for weather and unplanned stops. Store the accommodation’s permitted vehicle approach and parking instructions alongside the address; the shortest navigation route may not be the right way to arrive.