Just ordered a new head unit

[hammerfang]

i just ordered a new Pioneer DEH-P4700MP with a wiring harness and got it shipped for $155, new on crutchfield its $159 + shipping and harness. Anyway it should be here soon and im wondering what u guys think i should do next, my car is a 95 325is and it has the stock stereo, im thinking of getting the bavarian soundwerks speaker package for my car with the MB Quart speakers, but im not sure of two things, one should i stick with the stock 4" speakers in the back or do i pay the extra $120 for the 6"x9" converstion and speakers for the rear deck, also im not even sure if i should get the speakers first or if i should get some subs, im also looking at the bavarian soundwerks subwoofer packages, any feedback u guys have would be great, thanks