u can run one amp to 4 subs, but ur gonna have to do alot of amp bridging and its not gonna hit as hard as u want. Ur suppose to run one amp to each sub if u really want to get the true RMS outta ur subs. Plus u dont need 4 12's. most people think that, the more subs u have the better ur shit sounds, which is wrong. I can get one 12" that sounds better then 3 12"s combind. cost more for the 1 12" but it shits on anything u can buy at best buy or wherever. if ur starting out i would go with 2 15" kicker CVR's ($250 for 2 15"s on ebay) then work ur way up from there.
as for the box goes, ported slapp harder. they allow the sub to push out more air causing more bass, which to me, its sounds like u want a lot of it. Depending on how big ur trunk is and how much space u have for the box is really gonna make a big difference in the sound quality of ur subs and ur system in general.
ported boxes look like this...
and if u really wanna have ur system slappin, u gotta find out what u want ur box tuned at. anywhere from 28 - 33 hertz is perfect for CVR's. if u want low hitting bass go with a ported box tuned at 30 hertz.