Replacing some / all of my system 10! Any Advice?!

Hello all ,
I have had my GT-Four for 3 years now without a functioning sound system. The front and back tweeters will work on CD's, and only the front speakers (tweeters, mids and door speakers) work on the radio. :shrug:

I haven't spent too much time looking at what's going on with the wiring right now (maybe an hour or so trying to figure it out)

On that note, I'm considering replacing the amp / head unit and hoping that the back speakers work once I re-wire everything properly.. I want to get a slightly bigger amp just in case I feel like putting better speakers in the future, and I want a head unit with more updated options such as USB and aux inputs!
Any suggestions on what I should power the stock speakers with? Are they even worth powering or should I be buying all new speakers first?

I just don't know where to start haha.

I've got some quotes but I'm thinking of doing it myself to save paying labor charges :smokes:
What do you guys think I should be paying to have a job like that done at a shop? (head unit, rewiring a new amp in and buying the parts?)

Let me know if you have any advice or experience with the system 10 audio set-up, while I scroll through this audio section of the forum for as much information as possible!

Installing an aftermarket deck is simple. there is an extra harness behind the deck that you hook up the adapter to. You will then have a working stereo. what wont work is the door sub's and rear speakers. you'll need to run new wires to the rear to get sound. as for the door speakers you can run new wires directly from the amp.

^ that's the hard way to do it, if you buy the right harness it's easy.

DIY it and save some money, audio really isn't very hard it's just time consuming to do correctly. If you're going to replace the System 10 amp with something else then just buy that standard Celica dash harness and run RCA's to the new amp, and tap into the outputs to the speakers where the OEM amp goes. Or if you want to keep the OEM amp for a while, get the proper harness off eBay (some searching on here should net you the part #) and install a new deck and speakers. Personally I'd replace the deck first, then the speakers, then the amp.