Easy audio upgrade suggestions ?

I have stock audio setup from 2000 RS (radio plus CD unit, front, door, and rear window speakers).
its getting old, and won't play most CD's. Speakers still sound pretty good though.

I've never tried swapping out audio before, looking for something that is easy for a newb to do, and works with a USB stick and maybe iPhone input ?
any suggestions ?

Is there anything that is basicly just.... slide out the old, slot in the new? or do I need a bunch or wiring harnesses, and brackets ?

thoughts appreciated

cheers