UPDATE 6/8: The course is about to start. Sign up here if interested (it's free to audit, as I'm doing), and if you're taking it, feel free to be in touch.
This course looks promising: "Paradox and Infinity," at EdX, by MIT philosopher Agustín Rayo, and I'm planning to take it as the next step in my online math education. It looks like it will be lively and interesting, for instance based on this earlier clip of some of the material, and I've gotten some assurance from course staff that there will be opportunity to build math skills.
I'm also, when I have a chance, going through the self-paced Calculus One at Coursera, taught by mathematician Jim Fowler of Ohio State University. That's a subject I studied long ago and never really understood. Down the road, I expect to take courses in statistics, probability and more; as an economics major, I learned some statistics, but that was never a strong point of mine either. Given the general level of mathematical interest and knowledge among journalists, I'm hoping to be an outlier.