From Stwolfgang to Vienna by car, are there toll stations along the way? Is it enough to just buy a vignette (highway sticker) and put it on the windshield ?

No, it should be included when picking up the car. Just make sure and you can drive it.

Make sure whether the car includes the expressway toll when picking up the car. Some car rental companies only include part of the toll, and give you a list of expressways that are not included. If your route goes through these expressways, you need to buy expressway tickets in advance. They are sold at gas stations along the way, 9.2 euros for 10 days, and stick them on the car window. There are no toll stations along the way, but there may be police checks. Of course, you may not often encounter them, but if you are caught without buying, you will be fined 120 euros.

I was going the opposite direction to you, but the same route. When I entered Hallstatt, I passed a toll station and paid 5.5 euros. The locals told me that all vehicles passing through there had to pay a fee. I followed the Tongtou map, but when I passed the toll station, I should not have gone down the far right lane (the truck lane). However, my companion said that the vehicle in front of her seemed to have passed automatically, so she went back and paid the toll using the automatic payment lane, where you insert coins. By the way, I downloaded the Tongtou offline map, and on that section I couldn't find where to set the entire highway. Tongtou will give you the most beautiful Road trip route, so sometimes driving on country roads takes a little longer, but the scenery is really beautiful.