Also which ATMs are best to use?
ATMs in Austria are everywhere; the "official" ones, operated jointly by all Austrian banks, bear this green-blue sign: https://www.blende7.at/images/Bankomat/bankomatlogo.gif
Private ATMs work as well. Every ATM operator is obliged to display extra costs just for the withdrawal, so you are given the opportunity to cancel. This does not include any fees charged by your bank or credit card company.
The ATM fees are the same everywhere in Austria. They depend largely on your bank and the type of card used. Fees for credit cards are usually higher than for debit cards, e.g. for Austrian debit cards there are no ATM fees at all.
Should you hit a "cash only" restaurant, don't turn away, ask for the next ATM in the vicinity.
(There was a report of a family in this forum, having skipped five restaurants before they found one accepting credit cards.)
There is no need to withdraw large amounts of cash.