Hi rasof
,
Of the guides that you have listed, Official Guide 2016 is essential for your preparation. Official Guide 2015 might have some older questions, so that can be used for additional practice too. It is not a study guide and may not teach you much about how to strengthen your fundamentals, but it will give you questions that have appeared on the test and will give you valuable lessons from the solution of the questions.
You have a lot of time at your hands and many times this is counter productive. You would need close to 3 months to be well prepared for the test.
Regarding the other materials, there are primarily three methods in which you can go about with your preparation:
1. Classroom course
2. Studying from books
3. Online preparatory course.
Chose the one you are most comfortable with. Most of the courses including ours offer a trial period. Make use of that and see if the course fits your needs.
Once you are through with the concept building phase, I would recommend you to buy Exam Pack 1 and Question pack 1 from mba.com for additional official questions.
If you have not gone through the mba.com site, that should be the first thing to do. So that you understand more about the GMAT.
After that you need to follow a study plan to study effectively. Most of the people need 3 months to achieve the ideal level of preparation.
You can find various study plans here:
https://optimus-prep.com/free-gmat-section