Without amp and sub, how would you rate the sounds compared to the standard?
The
speakers I chose have a pretty strong low end response, so I don't find I miss the sub for the music I listen to. If you like to feel really deep bass (and I do mean "feel" not "hear") you'll want a sub.
As for the amp, you'll need one if you listen at high volumes, otherwise the built in amp will start to distort which is bad for sound quality, but will also shorten the life of the
speakers. I find having rear
speakers helps a lot to fill in the sound (I accept it doesn't help with stereo imaging). When I set the fade to just use the front
speakers, I can't get enough volume or bass without distortion.
The most important thing is careful installation. As in my links, I added some sound deadening, used very rigid mounts for the
speakers, and placed the tweeters on top of the dash (the original placement next to the handles is about the worst place to put them). You won't get a Ford garage to do that, and you'd have to pay quite a bit for a pro to do it. I suggest you do it yourself if you have any practical skills, or find a mate who's done it before and you trust to wield a screwdriver around your car

.
That picture was a "super capacitor" by the look of it. They are put between the amp and the battery to smooth out the peaks in supply and demand of power. Opinion varies on their usefulness.