1) Are you able to live comfortably off the salary?
That depends on the area you live in (I read that in many areas of California teachers have to drive for hours to get to their job because they are unable to afford a house near the school) and the number and age of people in your household (that changes all the time). Many teachers spend their own money on classroom supplies.
2) What are the gratifications of being a teacher?
Teachers usually love seeing their students succeed in learning their subject and become better persons.
3) What courses are of most importance to take in High School?
Depends on the subject you will get highly certified in. Math majors need strong math courses, science teachers need physics etc. In any case, a rigorous workload is the best solution.