Alpine are the best audio people around but you pay for it. They would be the best to go with when it comes to everything, subs, speakers and amps.
Also get a capacitor or even 2. You will need em if you want to keep the power and therefore sound stable.
Door card speakers are usually 6.5inch or 15cm. Get a pair that include across faders as you can also put in tweeters.
i would run seperate amps for the speakers and subs.
the power of the amps is going to depend on what watt you want. (say that quickly!)
Make sure your sub amps are bridgable as this will help you in getting the power you want.
Hope this helps, iv tried to be as simple as possible here but i can elaborate if needed.