thats a pretty big step for your first sub. Now if you get that you better design and build an enclosure for it or get some1 else to do it. regular high schoolers have low end best buy shit, so id say you should go with something around 1000 watts
re sx, fi bl, fi q, hdc3 just to name some loud ones. if u really wanta be king of the school just get one of those subs as an 18" and go from there. an 18" is gonna need to breathe 2 so u gotta have 4-5+ cubic feet for the sub. Id say you should go 15".
and what terra said(very important) if you dont have the electrical system to withstand it that wont be good, going as large as 1000+ you gotta run dual+ bats, 1/0 wiring, and you MUST do the BIG 3.