Your UK license will work here
You won't need a US license -- Actually there is no such thing as a USA driver's license. Each state issues it's own license, with different testing requirements.
Mark
Pick up the phone and ask someone who has been doing it for 22 years.
May I suggest that you pick up the phone and call Don at autotourusa - the website Michael published above. I have spent quite some time chatting with Don about my requirements for next year, and the advice and suggestions he had for me are pretty sound, to my way of thinking. Also the warnings he gave me, and things to consider which I had not even thought of. He struck me as someone with whom I can do business, though I have not yet made that commitment.
You will find his phone number on his website. If he is not there, leave a message or call back at another time.
Besides focusing on the purchasing, resgistering and insuring of a vehicle, I would ask him for advice for when you are ready to sell it as well.
Lifey