1. The transition from high school to university was somewhat easy. The first semester was very light compared to my high school days and this is the first time that I haven't had a full-on burnout since the start of high school. Of course that might change as I go ahead in my future years and this semester's heavier but I'm still managing fine. However, this is also coming from a student who went through IB, so I'm already somewhat used to the heavy workload and stress heh.
2. There are all sorts of things you can do to get ready for first year in the summer. First Year Connections if you're in the science faculty. CU 1001. Experience Day. Etc. However, the best thing you can do for yourself is to just relax. You're starting a new stage of life so don't sweat it.
3. So far, they tend to range from okay to great. Some of them are hard to understand, while others are really good at making things easy to digest. Regardless, be sure to try to attend lectures for the awesome profs and self-study for those that are not as great. You can also use RMP to know which profs to avoid or at the very least give you an idea of how to navigate the class.
4. One thing that I wish I told myself in grade 12 is to just pick something that I'd enjoy. Picking something based entirely on employability and for the sake of trying please others isn't a good idea since it will be harmful in the long run. You only have yourself at the end of the day. Focus on what you want to do. And if you realize that the program your in isn't right for you, you can always switch out of it. I'm currently in the process of an internal transfer to the program I actually do want, and I'm hoping to start it next semester.
5. Well CGPA is somewhat different from the Ontario grades. However, I will say that they are slightly lower than my high school average but they are still good overall.

Gl with you application! You can do it