Well im also gonna get the head unit for the mp3 playing ability. The headunit is supposed to help out some though isnt it? And do you guys think I will be good for now not replacing the speakers already in there, just going with 2 12"s, head unit, and amp?
As previously mentioned, if you buy amps for your front and rear speakers as well as sub, your receiver will be a stand alone unit. My suggestion is to disconnect the rear's completely, get a premium set of front components (like JL XR's or ZR's), and run them through a 300/2 amp. Then get a good sub in a ported enclosure (JL 10w7 or 12w7) and put a 1000/1 on it. This will most likely be out of your price range however the audio quality would be phenomenal.
-imo the rear's just degrade sound quality in the celica cabin (too much interference)