Re: USAID Attorney PositionsTrue. I think the ad lists a contact at USAID who may be able to answer the question.
If you haven't read Career Diplomacy, I recommend taking a look at that too. It has an overview of USAID and addresses some differences between the roles of FSOs in State, USAID, Dept. of Ag. and Dept. of Commerce. You won't find the specific answers to your questions there, but it does explain how the hiring practices, length of assignments and the like differ. It's a useful resource in any event.
Again, best of luck.