6x8's or 5x7s will work in your car...the only problems you might face are the depth of the speaker(from mounting surface to back of magnet). This is mostly an issue w/ the front speakers and clearance of the windows. Since you don't have the Mach460 stuff installing an aftermarket stereo will be cake.
To remove the door panels...take the trim ring around the door handle off by pulling it free...then the switch panel/door pull snaps out, you then should free the switches from the panel/pull. Remove the screws that are behind where the door pull was, any screw that is binding the panel to the door should be removed...i can't exactly remember how many...seems like 3 or 4. Also, w/ the door open feel to the fron edge of the panel and find the plastic body pin in the door jamb...remove it. Now the panel should be free...and just pull up and away from the door to remove. There will be other platic body pins inside the door panel..simply pull the entire panel. Reverse all this to put it back in.
2000 Coupe stock speaker replacement 
