I plan to take the AP US gov exam in the spring. Unfortunately, my school does not offer AP US gov. Instead, we have a regular, one semester, honors level government course (2nd semester). I intend to start learning all of the AP US gov information using Khan Academy and the AP site (practice questions and all that jazz), and then to review it all by using an AP US gov study book with multiple practice tests. I’m hoping to finish this all by about April, by which I will have also benefitted by having my knowledge supplemented by the honors level US gov course that I will be taking in school. My question is whether Khan Academy, the AP site practice, and in-depth reviewing of the material (as well as reviewing all of the essential documents and SC cases found in the AP US gov syllabus posted by the College Board) will be enough to sufficiently prepare me for the exam? If anyone who has self-studied for AP test (not just gov) has any insight, it would be greatly appreciated.
I am currently taking AP U.S. Government. I think your plan is great! 
It seems like you have a plan so that is good. The thing about AP Gov is that there are so many words and definitions you have to memorize. When my teacher was teaching us “linkage institution,” she specifically repeated that this term is made up and will never be seen outside of this AP class. The specificity of the FRQs is also insane, you need to meet specific thresholds based on the wording of the question and have to adhere to specific guidelines. It really is the specificity of FRQs that make it hard to self-study social studies exams IMO.
I took AP US History last year but my teacher didn’t teach practically anything so two months before the test I cram studied solely on Khan Academy and got a 5 on the exam. I was amazed at how similar the Khan Academy content was to the test questions, including the FRQs. I would recommend also taking a few practice test as well as Khan Academy practice to get a feel for the specific types of questions on the test though. I plan to go through the Khan Academy AP Bio, Stats, and Calc courses for my tests this year, too, because it really is such a great tool!