If you have to work while going to college, then I strongly suggest that you take whatever number of courses you can take each semester. If, for example, you have to work 20 hours a week then I suggest not to take more than 2-3 courses per semester. If you try to do more courses then you may not have time to study all courses, which may result in not getting good grades, which could end up discouraging you and unfortunately, it may lead you to drop college. And, you should never ever think about or be in a situation that you drop out of college. You MUST complete college even if it takes 6-7 years, given that you have to work part time.