Most car speakers are 4ohm speakers, and most off the shelf amps are for 4ohm speakers. check out alpines website for some combo packages, even if you dont want alpine it will give you a good indication on what to buy. also, dont go with what people say.. go and take your fav cd into the stores, and listen on the demo boards.. .what sounds good to me, might sound crap to you.. and vice versa.
any more info might want to go to http://www.mobileelectronics.com.au just go to the search and you find all the info you need
as for the subs, trust me when i say the type s subs are great, the two that i have, (the ones in the pics) (i photodhopped the pic thats y there are 4) have lasted me almost 9 years and produced a 135.5 Db in my old bluebird wagon... so yes there cheap. but they are proven, to me anyway. also i dont want huge 15's so 4 12's are a comprimise.