Hi,
I'm going into my third year in the math and stats program, so I guess I can answer some of your questions. However, I was in Science for first year, so I guess we will differ there.
First year math, I believe you'll be taking pretty much the same math courses as a first year science student, except you'll be taking 1X03 and 1XX3 instead of 1A03 and 1AA3. I hear the only real difference is that you go somewhat more in depth and the classes are smaller, so its more personal.
You should do very well in your first year if you've been doing well in high school. It's probably nowhere near as difficult as you've made it out to be in your head
Just to give you a reference, I got a 12 in every first year math course. Even second year isn't very difficult, as long as you keep up and do your work, homework, and recommended problems. I also managed all 11's and 12's in second year.
Third and fourth year on the other hand, I hear can get quite difficult, but I can't speak from personal experience on that issue.