How many courses can i take at another university as a visiting student, and still graduate from my mcmaster program?
is there such a limit?

What faculty and program are you in? And how many courses are we talkin?

The quick go-to answer is that it shouldn't matter, so long as you have fullfilled your course and degree prerequisites; obviously some programs in the health sciences and engineering may limit the amount of credits you can take elsewhere, but given the availability of those credits I'm assuming you're in hummer/sci/business, etc.

I think if you have a letter of permission for all of them you should be fine. Of course, it would be best to ask an academic advisor.