The math course you would be registering for would be 1A03, although the 1X03 and 1A03 classes were combined if they keep the program like last year's. They teach the same material, the different course codes are just to distinguish between students in the math and stats program and everyone else. That said, if you're interested in math you could try the follow-up, 1AA3, or linear algebra, 1B03. I took both 1A03 and 1AA3 and I loved both courses.
However, math is not required for your minor in comp sci. You can find the requirements for a minor in comp sci listed here:
http://registrar.mcmaster.ca /CALEN...nt/pg1201.html
All of my classes last year were in the Faculty of Science, so I'm not sure I can help you with electives. I've heard Latin was really good, but it's always full so I'm not sure you can get in. If you're interested in anatomy, KIN 1Y03/1YY3 are both excellent courses. Otherwise, I'm not too sure.
Good luck with your course selections.