Hey I'm from Austria so I can tell you!

They mean Wiener Neustadt for sure. There is a small airport there, in german called "Flugfeld". Vienna airport is a mistake, because as you said it is Schwechat, our country's main airport and there would be no space for that
Where did you get that concert, I am curious as I never heard any bootleg from BJ concerts here, sad but true

You can be sure that there are overdubs on most of the records.
Kiss even took studio songs and added crowd noise on Alive II, III.