It would be advisable. Going to a summer school especially during your last summer at high school will be very advantageous as it will not only help improve your english but also provide a smooth transition to your college life in the states.
Very important! As well as high TOEFL and SAT scores, your high school grades (including the grades for the first semester of your final year) do influence the decisions of the universities.
You don’t have to but it helps if you have a good counselor.
Yes, it would.
Usually, students have decided by the end of their junior year, but if you haven’t decided by then, it’s probably better not to hurry. Aim for a Liberal Arts department which will give you more time to decide.