You cannot, unless you take up a "permanent resident alien" status or become a naturalized US citizen, and take up permanent residence in one of the US states.
Not in the UK
I don't know about every state, but in most, no. You can get just a motorcycle license.
Not unless the particular occupational specialty to which you refer requires a drivers license to perform it.
Yes. If you possess a drivers licence, you'll have to get a motorcycle endorsement added to it in order to be able to operate a motorcycle.