I'm in the first year at another uni and this is my understanding.
1. Normally the first year marks don't count towards you degree, you just have to pass each subject,
The pass mark is probably less than 50%.
You maybe able to fail one and still pass the year.
2. You probably only need to buy the essential books, the rest are recommendations which you should be able to find in the library.
3. The lecturer should tell you, but it can be a mix of test and coursework.
I know it looks scary, but I think they will teach it without assuming any prior knowledge of the subject.
Most university maths departments have a support team who will help anyone from any course with maths.
4. Use the library. Look for second hand books from last years students.
5. If you're not happy, please go and see your personal tutor or course leader.
The university wants you to pass the course, they will help you all they can.