Are class notes enough to secure at least a 9 GPA at Heritage Institute of Technology in the 1st year of ECE?

Yes, they are enough but only if you do not miss a single class, and are very serious about every assignment and internal mark.

Your professors and seniors would definitely suggest you the reference books and you should their advice. Everything is not about marks. You should have surplus knowledge about your subjects which brings completeness into the course. 

Due to time limitations, everything cannot be taught in the class. Also, engineering is beyond your semester syllabus.