If math is your weakness, then the Manhattan math series very helpful. Another option is the Kaplan Math Workbook. Before attempting the
GMATClub tests, try to complete the OG books. When you're ready for the
GMATClub tests, I found it less stressful to treat them as a source for practice problems rather than as practice tests.
And this leads me to another issue. It seems - and I may be mistaken here - that you plan to rely on a good bit of practice tests for your overall preparation. If I'm correct, then a word of caution: practice tests are important, but please don't let them consume too much time from reviewing guidebooks or problem practice.
I hope our dialogue was helpful!