which hotel location in Budapest . . . and other stuff

The Raday utca location is better situated as it has access to the Kálvin tér metro station and the 47/49 Tram Line.

The other location is near the upper end of Rákóczi út which is a fascinating street with some interesting buildings and land marks, but it's also a bit dirty and not nearly as well connected to the sights.

We stayed at the Raday street Ibis for 6 nights, in June. Great location, about 50 yards from the metro stop.
Many restaurant options nearby.
Room 812 is large,2 beds,2 closets, and quiet, located in the back of the hotel.
We loved it.

When I attended the opera--at the official opera house in 2016--I wore a jersey dress and heels, which I justified bringing because I was also going to a musical at the Operett. I had a seat in the main section front and center and people were wearing everything from black tie, gowns and jewels, dressy pantsuits, slacks and button-down shirts, jeans and even a hoodie. So, at the Erkel I think you will be fine in slacks or jeans and a nice top.

Since you are a habitual returnee to Budapest I think you have chosen well to go to the Erkel. You will be joining in on an event which will be overwhelmingly a Hungarian cultural event with few tourists present. You will gain an insight that most never have the opportunity to gain. Heck, you will learn a lot more than most tourist just getting to and from the place. Remember, Budapest is safe, just keep repeating that to yourself and try to look like you know where you are.

I don’t comment on women’s clothing. I learned the hazards of that in my youth. Yes, you may see someone in a hoody, but that more likely at the State Opera, and most likely a tourist. Hungary is one of the most conservative cultures on the continent of Europe. So much so that they get criticized for it on the world stage. So, without doing any other research I would begin the decision making from that basis. Then, do a little research. I love Google. If you want to know how people dress in one situation or another, then take a look at the photos. Unfortunately, there aren’t any really good views of the audience. But this gives a good clue: http://www.lifebitesnews.com/userfiles/ErkelTheatre_Color_Budapest15(1).jpg Copy it to your computer and blow it up.

I’ve been to about a dozen performances in Budapest; but I haven’t been to the Erkel. But the State Opera, Operett, Liszt Academy, Palace of Art, and a couple of Jazz Houses all shared one thing in common; folks dressed well. Much better than in the theater house in my home town here in the states. I wouldn’t go to an evening performance in anything less than a dark sports coat and dark slacks; and for an opening night it would be a dark suit. It is pretty impossible to over dress and in most cases those that dress well are appreciated by everyone.