We were in Salzburg on Easter, April 1, 2018 and it was glorious! We went to Easter Mass at the Cathedral and enjoyed the beauty of the art in the Cathedral, along with the incredible orchestra and choir! Some of the music was written originally to be performed in the Cathedral. The service lasted two hours, for which we stood- that is evidence of the experience- and- we are NOT religious. [We should have arrived about 20 minutes earlier for a seat.] As the service ends and the congregation exits, the sounds of church bells ringing fill the square.
Restaurants were open, and the Fortress. However, many of the specialty shops were closed both Easter Sunday & Monday. The Easter shops were open, with all the hand-painted eggs- which we were able to transport home intact.
I believe there are Easter markets in Austria the week before Easter, but we were in the Czech Republic then, enjoying the Czech Easter markets. Funny- much is written about xmas markets, but not Easter markets.
We were in Hallstatt the day before Easter, and the town was very sleepy and not all the businesses were open- this was late March, and early in the season. I can't imagine Hallstatt being as glorious as Salzburg for Easter. However, the Hallstatt Salt Mine Tour is a must!