I notice that you want to start with fundamentals before you actually begin preparing for the GMAT itself. I would say that you should brush up on those fundamentals using something that is GMAT-specific. You do not want to study "math" in general, rather you should focus on the things that will actually be on the GMAT.
The materials that I am most familiar with are those that I use on a daily basis, the Veritas Prep materials and the Official GMAT materials by GMAC. The Veritas books have "skillbuilders" at the beginning of each book. These skillbuilders are designed to take people from "I have not done math (or grammar) in 10 years!" all the way to "Okay, I am ready to look at actual GMAT problems now."
For example, I just worked with the Arithmetic book in my live online class a couple of nights ago. The skillbuilder for that book is 90 pages long. It includes quizzes to make sure that you are up to speed on the concepts before you get going on the actual GMAT problems.
With most of the 12 Veritas books there is a skilbuilder. What I like about this setup is that you go through the skillbuilder for a particular subject and then you work on questions for that subject. I think that this is more effective than just studying "math" and "grammar" in some general way. What I am saying is that you can work on the fundamentals, while you actually study specifically for the GMAT.
I have written about the Veritas materials because these are the ones that I, as a Veritas instructor, know best (and because I think that they are the best). But overall, what I am trying to convey to you is what you should expect from any materials that you happen to choose. You should demand that your prep materials take you all the way from "I know nothing about this!" to questions that are above the 700-level. While the Official Guide to the GMAT is a great resource, it does not really help someone re-learn the fundamentals and it does not have enough really tough questions.
Here is a quote about the Veritas books from a recent review
"I found that Veritas had more advanced homework problems than [a competitor] and had developed more content outside the OG guide." It is possible for you to be working on a 90th percentile GMAT question and still learn a basic concept
at the same time. You should be able to say "Oh, I see, you can combine these exponents in this way" (basic concept) and "I also see how the GMAT makes this question difficult and I will know how to approach it in the future" (advanced GMAT understanding).
Like I said there are many courses, books, tutors and resources out there for you to choose from. What I have discussed above is what you should demand from the course, book, or tutor that you select.
Best of luck getting started. Keep posting any questions you have and the BTG community will do our best to help.
Here is the link to the Veritas books on Amazon
https://www.amazon.com/Veritas-Prep-Comp ... +prep+gmat
Here is the link to the course reviews page here on BTG
https://reviews.beatthegmat.com/
And just for fun... here are links to three articles that I wrote about "lifestyle" things that can really impact your GMAT preparation. You might as well start out right on your GMAT preparation! And remember, have fun!
https://www.beatthegmat.com/mba/2011/02/ ... asking-now
https://www.beatthegmat.com/mba/2012/05/ ... e-the-gmat
https://www.beatthegmat.com/mba/2011/03/ ... n-the-gmat
