are there requirements for any travel documentation (besides passport) from US to germ / switz / austria?

No, unless you are staying for more than 90 days. Go to travel.state.gov for info on entry requirements for all countries.

International Driver's license if you plan to drive in Austria.

For driving if that is an issue I suggest you know the difference between an International Drivers Permit and an International Drivers License.

Thanks all...appreciated. And will investigate the driver license matter.

Germany and Austria are both in Schengen - you are allowed to stay for a total of 90 days in any 180 days in the whole Schengen zone. Switzerland isn't in Schengen and you can stay for 90 days. Just your passport needed - no visa.

You can get that licence/permit at AAA.

Just remember when driving in Austria, you have to stop at the border and purchase a toll sticker for your car if you intend to drive on the auto routes. I understand you can get them elsewhere, but we stopped at the rest area at the border and bought a 10-day sticker. I'm not sure what denominations they come in, but don't get caught without one.