1. I think studying in college is a way harder, because In most of cases you need to look for yourself as an adult and study well if you want to graduate.
2. The main advice for mid-school student from be is - hard work and be aimed at your dream, this is gonna be your motivation till the very end.
3. Well it depends on human being and his active and social skills, and of course on importance of its job. But from my point of view if you will be a real professional you will reach all your goals include a good job for sure.