Running speakers out of phase will blow them. From a local shop here.
You want 10" subs for rock, 15" subs for rap. And 8" subs for sound quality. From same local shop.
Kicker subs sound better for rap, while memphis and rockford subs sound better for rock. Same local shop.
You wont hear the peaks and dips in music without a cap. Same local shop.
Oh yeah, said local shop is California Car Stereo.