I'm a senior at a private research university that has an accounting doctoral program:
BS Accountancy
BS Economics
GPA = 3.6
Quant classes taken: Calc I, Calc II, Linear Algebra, Intro to Sampling, Econometrics
Research experience: I was an RA for 3 accounting professors since I was a sophomore, and one of them supervised me while I wrote my undergrad thesis. Working knowledge in Stata, R, Python (Are programming skills attractive to admissions?)
Teaching experience: TA'd for financial accounting for 3 years
Other work experience: A few internships with accounting regulatory bodies, and I'll be on the CPA track with Big 4 audit after graduating

I haven't taken the GMAT yet and know the magic number is 700. I feel like my weakness lies in my quant skills even though I have an econ background. Would it be beneficial for me to take some more math/stat/econ classes at a local community college or online? My LORs will be from the 3 accounting professors I've worked with and they're all research active. I'm primarily interested in financial archival research, but considering my work experience, auditing research also sounds appealing.

Are there any other things I can do to better myself? I'm hoping I'm good enough for the top 20.