English is a required subject in school. Almost anyone under 40 has some proficiency. I live here, i speak about 30 words in Hungarian. Not good, but not a problem either.
The Hungarian Forint is the currency. Today it is about 340 to the dollar. Yes, you can pretty much get by on a credit card alone. But you might run into a rare exception or want to leave a tip (tipping is part of the culture, but its different than the US: another topic)
I think having 9,000 or 14,000 ft in your pocket isn't a bad idea. 9,000 is about $25 and 14,000 is about $40. Why the strange sums? Because when you use the local ATM to get it you will get some smaller bills. (Forint paper comes in 500, 1000, 2000, 5000, 10000 and 20000 notes).
I suspect you will not have trouble getting rid of most of it your last day and will only go home with a small souvenir.
I understand they don't yet use the Euro.
The statement assumes that the want to use the Euro. Hungarian nationalism is yet another topic.