You're good with Python / R, no need for C++ in my opinion. Other than that I agree with the other posts. I wanted to suggest that you try out this book, which I found really really helpful:
You'll need to start by understand how models are fit to data, which is typically done via maximum likelihood estimation. This will show you how to do that. If/when you move to Bayesian approaches, understanding basic MLE really well will be super helpful background.