The insurance companies will generally ask whether you have a full UK license, and if so, how long you've held it. Being British, I have no experience of how they'll load the premium for non-UK licenses, but as the others have said, you can be sure it will be expensive, at least at first.
It always used to be the case that premiums dropped substantially at age 21, then again at 25, as many younger drivers found it much cheaper to just be included on their parents' policy.
Insurance quotes really do vary drastically from one company to another though. You may find yourself better off going to one of the more specialized companies rather than the run-of-the-mill ones who have the big ads on TV.
With regard to actually buying a car, you don't need any driver's license to do that, UK or otherwise. Whether you buy privately or from a dealer, you just fill in the part of the registration which is sent back to DVLA (equivalent of the DMV) and they mail back a new registration with whatever name you've put on it.