Reading the other current posts begs me to point out a few things relative to what RS people are concerned about..
COVID
Hungary has no COVID paperwork to complete or websites to register with and no EU COVID pass or certificate is required. You will need a PCR test 72 hours prior to arrival from the US. If coming from the EU, generally speaking, nothing is required.
TRAIN or PLANE
Other than Vienna the nearest major tourism city is maybe Prague which is 7 hours on a train; which I figure to be 8 to 8.5+ hours door to door for an experienced traveler. Add 30 minutes if you are not familiar with European trains and the public transportation or taxi service at each end.
Upon arrival the train station is sort of in the center of Budapest, but possibly not the center of the part of town you will be staying in. Public transportation or taxi; both may take up to 30 minutes to get you to the hotel. Be sure you understand the luggage rules on the public transportation and be sure you purchase a ticket or pass and validate it. Okay let’s add another 15 minutes if you are using public transportation. For a taxi from the train station call City Taxi when you arrive. They will have a car there within 10 minutes. The taxi stand is on the north side of the station.
By train you get to see all the wonderful places in between like an experienced traveler; plan on an additional four days of travel to do so if you are coming from Prague; but not at the sake of cutting Budapest short. Not a whole lot to see out the window along the way except a very large, very angry looking bird just across the Hungarian border. The train from Prague will set you back about $25.
By plane the same trip from Prague is maybe 4.5 to 5 hours door to door if you use a taxi at both ends. If you check a bag it will add maybe 15 minutes to the time to get out of the airport. The flight with carryon only will set you back about $75.
The airport is 30 minutes and $25 from the town center by taxi. Taxis are somewhat inexpensive, well regulated, clean (follow the arrows on the floor to the Kiosk outside the arrivals hall and a very nice young lady will assist you). Or you can take a shuttle bus or the public transportation for a fraction of the cost. Figure an hour, maybe longer, including time to purchase the ticket and wait for the next one leaving and the drive time. With public transportation also count on a decent walk.
LUGGAGE and PACKING
Luggage from Walmart within the airlines size and weight restrictions is more than adequate for the short trip from hotel room to taxi to plane and back. Or upgrade to Target luggage. Pack it any way you want, no one will care. And if your hotel room sink is too small, I can recommend a good next day laundry service.
If you are going someplace nice, like the theater, please do bring smart clothes. People here do still dress up a bit for such events. The theater a few nights ago, 75% of the men had sports coats, 25% were tourists.
AMERICAN STYLE or EUROPEAN STYLE HOTELS
When booking a hotel, look at the photos of the rooms in each hotel. You will probably want to choose by bed linen type. You can see that in the photos. You might also consider the futon beds at the very nice Thai Hotel on Andrassy.
For breakfast I believe you can get fried eggs at Café Vian. Omelets, scrambled eggs and boiled eggs are readily available at most breakfast stops. Or you might want to send the K&K Opera Hotel the question, as the last time I stayed there they had both fried eggs and decent American style bacon at the breakfast buffet. Starbucks are everywhere for the coffee hounds, but I am good with what ever the local eatery is offering.
MONEY
Credit cards are almost universally accepted. Otherwise hit the ATM machines.