Math skills are very important indeed, so it's good you're taking care of that. You didn't mention your skills with statistical software, that's also something that is better to develop before starting a PhD.
A GMAT of 700 probably would be acceptable, it's usually the minimum recommendation. But it's not exactly an impressive score, as many PhD applicants have a score like that.
Then you asked about things that will make you stand out. GPA, GMAT, and coursework matter, of course, but I think they are more about showing that you can deal with classes, or something like that. They still are not good enough to show that you can deal with research, and that's the focus of a PhD. So, I think that applicants who stand out are usually those who also provide some evidence of that. Maybe because of a paper they have published, experience working as RA for a professor, a conference presentation, or strong letters of recommendation from professors who have a good reputation with research, for example.
About a list of schools, that's something that nobody can really do for you. It's very hard work, I know, but it's hard work you are expected to do. To check the universities, check the faculty, check their research interests, check their papers, and see how your plans match what they are doing. If you think you can extend the research a professor has done, for example.
Why did you apply to a specific school is a very important question you are expected to answer. If you just tell that it's because the university specializes in behavioral accounting, then probably it is still too generic, and answer that would apply to many different universities. And you only will be able to provide an excellent answer if you really did your research about the university's program.