F2 is dependent to F1, so as long as F1 is in legal status, F2 is in legal status, but it also means if F1 is out of status, and so is F2.
So, to question 2, it is obvious that when OPT expires, your F2 status is out of date, so you have to reimburse your status or go back to china within 60 days.
To question 1, probably the answer is yes. you are ok.