What size speakers do i need for an 08 panel the front i think are 6 1/2 but what size are the speakers on the rear doors?

 

Same size, 6.5". You can use the same speakers all around if you like, in fact the rears have a little more depth, you should have plenty of room for most aftermarket 6.5s.
Do you have the base system, or the upgraded pioneer speakers? If you have the base system, you will need to make or buy speaker adapter rings.

 

I just have the cheapest system lol now I also heard that there is no RCA cable or something on my headunit so i wont be able to hook up my amp and sub is this tru?

 

You will need adapters or make your own baffles for the speakers to fit. You can also use a line out converter to hook up and aftermarket amp to the factory head unit. They range from $15 and up.

 

Some amps also have speaker level inputs instead of RCAs.