2000 4runner speaker install

I'm not a complete n00b to car stereo but the 4runner is kinda new to me. It was a huge headache getting the right harness for the deck until i realized there was an amp behind the ashtray!

anyways I need help with speaker install. I'm primarily worried about the front but will do the back doors as well if i have the cash. I need tips.
How do i take the door panels off?
how large of a speaker can I mount?
can i do 6.5" components in the front 5.25" in the rear? and how deep? I'm interested in ID chamelons.

and the biggest question is with the 2 speakers in the front. there is a tweater up top and a speaker down low. how are these wired? is there 1 speaker wire coming from the dash to the door then it splits off to the tweet and driver? or are there 2 pairs of wires going through the door.

any help or links to sites woudl be apreciated.

thanks