Please tell me what you think of this set up and how it could be improved.
'94 Toyota Celica
2 Infinity Kappa 120.3 DVC subs (12's) in a Bassworks box.
Ultimate T3-500D mono amp
Pioneer DEH-P3900MP mp3 Deck
4 stock 6.5" speakers (they are better than average quality for stock)

 

Nice start for sure

 

Yes, its a start, but not quite a system.

Be care ful about running factory speakers off your head unit. A lot of factory systems have gone to 2 ohm speakers and that will fry most head units, I don't think the pioneer has overcurrent protection, just thermal shutdown.

12-13 year old stock speakers will probably quit soon anyway.

You really asked for opinions, didn't you? And you are in the SQ section?

Nothing wrong with the pioneer, ultimate or infinitys. But you really need to replace those factory speakers and get another amp.
That pioneer deck has 6 rca outputs and built in crossover. Celica is kinda small for 4 channels, so i'd give up on rear speakers, put all your money into a good set of 2 way component speakers and a 4 channel amp to run them active, making use or the crossovers in that deck.
TS-C160R & TC6004 would work well.

 

Ya I will get speakers in the future but do you think i could use the stock ones for 1 year because i am low on $$$.

 

I think you'll find your stockers will be holding your system back and you'll get the upgrade bug soon enough.

Plus you'll want to watch that the extra bass from those subs doesn't mask the audible distorion of overdriving you stockers also if you really turn it up.

 

I'd say get a 4 channel amp now if you can afford it... You can get a little more out of those stock speakers, and once they die, you will already have sufficient power for your new speakers.