as for some of the other questions, window and hatch rattle is a common occurance on integras.. do a search for possible solutions.

a/c will noticably affect gas milage, but it's nothing major.

as far as your lights dimming with deep bass hits, that just means your amp is drawing a bit too much power. you may want to look into capacitors or maybe a stronger alternator.

once again, try a search.. lots of these questions have been covered before.