Intertational School Bus Audio

So...The football coaches at my school bought an old school bus for a "team bus" that they sit on top of and watch every game. So they told me to get a couple of friends together and they want us to customize the interior to make it a lot cooler. So I went and looked at it last night. So far they removed all the seats, have a couple of couches in there, and on the radio they just pulled it out and cut the wires haha....So I looked at it and can't find any of the speaker wires. So we decided we are going to buy 4 new speakers and mount the boxes for them between the celing and wall. What I can't decide is speaker sizes. I was thinking 4 6x9s in the interior. What do you think?
-Thanks!

6x9s What is wrong with you???
If you want some good sound go with some bump go with 4 12 inch subs.

and no mid/highs? if you aren't too concerned about quality (which i'm guessing not in a bus) 6x9s would be fine, but i'd go with more like 8-12 to cover the whole bus. if you want more bass you could add subs.