but i can understand from experence it is very hard to follow my advice when it comes down to it. so your goal would be to get into a position where you guys can stay in touch outside of school. another thing is all of those signs you mentioned are very interesting like they said b4 they could mean she wants to be friends or something else, in either case she likes you which is good.
as for the quite person thing i know its tough, trust me i was really really quite in highschool, but you have to break out of it. i guess it had to take the incident i mentioned above to make me do it but still i did. and i went to a highschool of 400 too, my class had 60 students in it.
oh another thing my advice b4 about showering her with attention that might be a bad idea, i cant call it cus i dont know you or her. these are the two possible situations and you can decide what to do. she will either like you for it because unlike other guys you are interested in her interests and who she is. the other possiblity is that she will get annoyed cus every body is always bothering her about that kind of stuff and she doesnt like to tell everyone who she is. if that is the case what i would suggest is to find a common ground and use that a a starting point and spread from there. or try my trick where you find something unique about you and talk to her about it.