rite! as u got a wide selection there, i would jus go for 1 sub, to giv ou that bit of bass when you need it, as in listenin to your rock!!
but id spend th most money out on at least a pair of 6'9, and maybe push the boat out and go for a set of front door speakers. your need a good amp too, dependin what wattage sub you go for! but one tip i will giv, make sure its all the same make!! my personal fav is vibe!!! brilliant base!!