Applied math PhD programs - no. of courses to counterbalance low GPA?
I would be surprised if the admissions committee paid that much attention to a number determined so many years ago. First of all the math GRE is extremely difficult and demanding, and if you do well on it people would notice. I would say if a professor looks at your GPA and has some concerns and then turns to your math GRE and sees that you scored 65%, 70%, etc. their fears will be quickly allayed and forgotten. Probably a GPA above 3 would be good but a few recent courses in senior level or beginning graduate level mathematics with an A-B in all of them together with a letter of recommendation from one of the professors who taught the class would be much more influential. There are so many factors that the admissions committee has to balance when trying to decide if a person is cut out for research, it would be silly for them to focus unduly on one thing like GPA.

My one suggestion is that when you mentioned your coursework you mentioned mostly applied courses. The admissions team will likely be composed of analysts, but also algebraists, topologists, logicians, etc. It would not hurt to flesh out your resume with some proof based courses: an introduction to abstract algebra, an advanced linear algebra class with proofs, going beyond intro analysis, things like that.