Any tips or special things to know for driving in Austria, Slovenia, or Germany?

Ahoy all,

My family and I will heading to Vienna next week for a few days. On our last morning we'll be getting our rental car (yes it's an automatic) and driving down into Slovenia for a few days, then back into Austria more on the western side for a few days, then into southern Germany for a few days, then on the last day we'll be driving to the Munich airport to return the car and catch our flight back home to New York. I've got my international driver's permit, although I've yet to ever be asked for it.

I already drive around New York City on a daily basis and it's no big deal. We also did a road trip around France including Paris last year which was fine (although I did mess up the priority on right thing once, and mistakenly went through the transponder only lane on the highway with just a ticket), and around southern Italy and Sicily the year before that which was also fine (even though drivers in Palermo are way wilder than what most of NYC has to offer).

So I'm not too nervous about the actual driving, but in my experience there are often more local rules and customs that drivers need to be aware of (yes I know not to hang out in the left lane). Like for Austria, I'm reading that cars need a "Vignette" which I guess is a sticker that goes on the windshield. Do rental companies typically supply this (we're renting from Sixt)? Or do I just buy one from a gas station and slap it on there and go? Looks like Slovenia also requires one, but theirs is purely digital, no sticker.

Any other particular rules or things to note that might be helpful?