Honestly, I have no idea how dual citizenship would affect you.  Your best bet would be to look at www.academyadmissions.com or www.afrotc.com.  If info is not on there, those sites have contact numbers and e-mails.

You will need to move to the US, because all the ROTC detachments and the Academy (there is only one US Air Force Academy) are in the US.

It is good that you are thinking about this early, because there may be problems with having dual citizenship.  You may be required to renounce your UK citizenship, but I do not know those regulations, so that is a complete guess.

Some other resources you might find helpful are www.serviceacademyforums.com  www.forums.military.com and www.talk.collegeconfidential.com (Service academy sub-forum)  There are a lot of knowledgeable people on those sites.