Grades are not everything./Getting good grades isn’t everything. Both are correct. In your first sentence, you are referring to grades (of two or more subjects) as a plural noun. In your second sentence, "getting good grades" refers to a single event, and you are right to use a singular verb "isn't". As an analogy: Good reviews ARE important. Getting good reviews IS going to help you.

Yes, looks good! (And I agree :)