Couple questions about USA collages for international students

Hello I'm Turkish 12th grade student right now and I want to apply USA colleges and there is some points that I couldn't understand or to clarify. I read faq. I will use Common App to apply.

I didn't do too many activities due to lack of opportunity that given me. Is it a real disadvantage?

What is graduating class size? Is it 12th grade students in my school?

As I said, I'm 12th grade student, I have to apply to colleges until this january right?

My school doesn't give gpa and other stuffs, i will leave it as blank right?

In the course section, Will I chose my all lessons that i will have in this year in school?

Am I suitable for write activites which isn't official like something I can't prove?

If you wish, I'd like to take some advices generally except the questions.