I don't know about V-Pay (never heard of it), but the main card companies (Visa+Mastercard) are accepted at most places. The place I really need cash are street vendors and bakeries, but I don't carry much with me otherwise.
Don't use EUR! Even though restaurants and some shops accept it, they change at a terrible rate (like 250 HUF/EUR)! Even the infamous change at the airport is better than that. Anyway: if you arrive by plane, only change some for the taxi ride (700+300/km) or train/bus at the airport. In downtown, you'll get sensible rates ( https://correctchange.hu/ shows at the moment 317.1-319.4+tax ) so you won't lose much even if you have to change it back later. But you can use your card with probably similar rate (or the aforementioned Transferwise).
Eating: 1500-1800 HUF for a decent meal at a not too fancy restaurant. Of course, this will go up steeply if you sit in a fancy place or too touristy area (Vaci utca, or the castle). Price of drinks varies even more. If you know what you want to see, museums tend to have english web pages, with prices, so use it. ( e.g. 1600 HUF https://mnm.hu/en/entrance-ticket for Nemzeti Muzeum, 1800 for the permanent exhibition at Nemzeti Galeria https://en.mng.hu/tickets/ etc. ) Most museums are open on weekends, but closed on mondays (or some other day of the week), so be prepared, and make a different program if necessary. You can use your mobile data (EU roaming) without any additional charge, so do it.
There are some nice open places (the castle, Hosok tere, zoo, etc.), so the forecast might get handy. ( met.hu, koponyeg.hu )
Also, don't invite suspiciously friendly sluts for drinks, that might be a scam. (I've read about this a few years ago, and don't know if the police managed to solved it or not.)