That's something you should talk about with your supervisor or graduate advisor. It's difficult to say whether that many course hours are going to be too much as not all graduate courses are created equal and not all graduate student workloads (in terms of TA or marking assignments) are equal either. Nor do we know how much progress you're expected to make on your research project over that time.
When I started my MSc, we were told not to take too many courses because we were expected to be spending time doing independent reading in our own fields, but this can vary from program to program.
The other factor to consider is yourself. Do you typically perform well when challenged with an above average workload? Some people do with an extra course or two to worry about. Others seize up and can't deal with the stress. Some people have no clue which category they fall into because they've never challenged themselves.