The currency in New York is US Dollars. You shouldn't have a problem getting hold of currency anywhere in New York. There are ATMs everywhere and most accept international cards. Major credit cards and debit cards are accepted in hotels, shops and restaurants, and if you do need to change some currency you can do so at most banks.
+1 for the USA. New York dial codes begin 212, 718, 917, 347 or 646.
The UK has a reciprocal visa waiver programme with the USA which means that most valid UK passport holders will not need to apply for a visa if they plan to holiday in New York. However you will need to apply for authorisation through the ESTA (Electronic System for Travel Authorization) before you can fly ? Click here to fill out a form and apply online. The process takes a few minutes and cost $14. Once you have your authorisation it is valid for the next two years.