pull the speakers u have now. purchase a set for ~100 and install that upfront. this way you’ll have normal sound there. next step is to build an enclosure and obtain an amp for the sub. once all thats in, you can add rear speakers if you still want those. i have no rear speakers in my car. theres just the two mids and two tweeters and the sub. take it one step at a time and each time it will continue to provide at least decent music with each consecutive step making it better and better heading for the full setup.
Pioneer Premier TS-A702C at Onlinecarstereo.com hows that look? i have a pioneer head unit so i like to stick with matching things (except the JL subs lol) or do i want like a 3 way speaker?
edit: here is a set of 4 ways Pioneer TS-A1782R at Onlinecarstereo.com