Yeah, I only did the fronts in my Golf :)
Does show up how poor the rear speakers are comparitively to the uprated front ones.
I'd recommend sticking with one brand for front and rear, just makes more sense.
For my hertz one you just trim the tweeter covers on the car to fit the hertz tweeters in straight away.
the larger 16 inch speakers bolt up with the adaptors.
The worst thing is trying to mount the crossover units as they're so big!! take the big covers off.
No idea really on that stuff, I am not that good with audio, only what my buddy Jairm tells me and what i've found personally.