My personal opinion is that it is usually better to wait until you have the strongest profile you can get before applying. This should improve your changes of being accepted, and of being accepted by a better school. But I'm not from Accounting to know if Calculus II will make much of a difference or not. It looks like that from what you wrote.
Being an adjunct professor can add strength to your profile. Even if the focus is on research, teaching experience still has value, and some professors really like that for several reasons (trust that you can handle TA work they assign, better communication because you can better understand what they need for their classes, etc.)
I know the Accounting PhD students here had a very hard time with the Econometrics courses. So, Econometrics is important, and you better be prepared for it. I don't know if an online course would be ok or not, maybe it is if the course is good.