Go here and click on car audio.--->
http://www.crutchfield.com/
You can atleast punch in your car to see what size speakers your car has. That's all you really need to know. Any speaker will work for the most part as long as it's the same size. Then you would want speakers with the proper watt rating that can handle the amp.
I think you might have 6"x9"'s all the way around.
As far as an amp, you'd have to relocate one into the trunk. The only direct replacement one would be from Toyota and it isn't worth the price.
I just put a factory Delphi replacement amp in a Suburban and list price was $700!! You can go to BestBuy and get 3 times the amp from Sony for $250.