I would dress in Sunday attire.. khakis and a polo will be fine.
I personally don't think it is too early because if I recall correctly for AROTC they open the files in Feb. your jr. yr.
I would suggest that if you have the chance to call on Monday and ask to meet some MSIII or IV cadets at that time.
Dets have unique personalities, just like every college campus has a unique feel.
Ask your folks to meet you somewhere later on campus (student union, etc) while you do this portion. The reason is simple, cadets show a lot of respect to an older generation. You also may feel more uncomfortable asking certain questions with your folks there...i.e. are you really going to ask will I have time to play Xbox with my friends? If they are not with you it is a peer to peer conversation.
Additionally by meeting them somewhere after, you get to walk the campus by yourself like you would next Sept. I have 3 kids and have done the tours, college kids know you are in HS, it is a blaring sign...Mom, Dad and kid = hs student. Kid by their self is not the same, you blend in with them. You get more of a personal feel regarding your future. IMPHO, I also think it is a great academic motivator at your age. Now it is reality and you can taste it because for 30-60 minutes you were just like any college kid on campus, freedom you never envisioned. That SAT score you need for admission is your goal.