Hi Bae!
As everybody else here has said, doing well in actuarial studies is definitely something you can achieve with hard work regardless of your background thus far. Past successes in maths are nowhere as important as your current desire to work hard.
You are absolutely correct in your suggested pathway for first year, and it is definitely the recommended choice.
In your first semester, you will have to do Introductory Microeconomics and Accounting Reports and Analysis as core commerce subjects, as well as calculus 1 and a general breadth subject.
In your second semester, you will have Introductory Macroeconomics and Introductory Financial Accounting to complete, as well as Calc 2 for your breadth. Introduction to Actuarial studies, while not compulsory, is definitely strongly recommended, if only to give you insight into what being and actuary entails.
Regardless of whether or not you choose to continue, going with the actuarial pathway in first year will give you a strong and broad base for your BCom degree, and you will be free to choose whether or not you want to continue without incurring any financial or academic penalties. Besides, you won't know whether it's for you until you try it!
Feel free to have a read of our subject review as well if you want to know what the subjects in actuarial studies cover
http://www.melbourneactuary.com/study/subject-review/Good luck!
ASS Representative