My son is in high school and throws a lot of 'raves'. Let me say that while the system you've got spec'ed up above is certainly going to work, it's a bit cumbersome, complicated, and expensive for the application you mentioned. What you're trying to do can be done a LOT simpler and for much less dough.
Cruise your local craigslist or guitar center for some used, powered, PA speakers instead of fooling around with amps and preamps. Most of what you'll find, you can just jack an Ipod or laptop right into them using an adapter, add power and party on. If you really want to go cheap, just rent the same equipment...lots of people do that. Having all that equipment investment, owned, stored, etc for occasional use can be problematic. Resale value is poor on new equipment, used holds it's value OK.
I've got a setup of 2 Behringer B315D's, a simple 12 input mixer (for teen garage band use) and cables that we use quite a bit that all in was under $500 - it was used, therefore cheaper. Later added a 31 band Behringer EQ, a big 18 inch PA sub for the boom factor, furman power, etc, but we got by without the extras for a LONG time and many a party. It's no hi-fi audiophile system, but it rocks hard, loud, durable, portable, and for hardly any money it's a perfect party setup. Would be good for outdoor movie night too!
Behringer gets a lot of flack from the Pro Audio snobs, but frankly, I think they are just fine for casual dj stuff. For the money, it can't be beat.