Candidly, I believe in starting early on the SAT and ACT exams on the theory that familiarity breeds better scores. DO study for the exams and DO be familiar with how the exams are scored. Another reason for starting early (by late sophomore year) is that NAVY will be looking for scores when you apply for NASS.
Regarding attire for interviews: For your MOC interview(s) I would recommend coat and tie/good dress or pantsuit. For your BGO interview I would expect you to be dressed in at least dressy casual - everything clean and in good repair, hair cut, freshly shaven, etc. If in doubt, ask your BGO what he/she prefers; if you are going to wing it, err on the high side. Remember, you have only one opportunity to make a great first impression. Best wishes to all of you.
Regarding attire for interviews: For your MOC interview(s) I would recommend coat and tie/good dress or pantsuit. For your BGO interview I would expect you to be dressed in at least dressy casual - everything clean and in good repair, hair cut, freshly shaven, etc. If in doubt, ask your BGO what he/she prefers; if you are going to wing it, err on the high side. Remember, you have only one opportunity to make a great first impression. Best wishes to all of you.