I think the front stage is a little more important, since you spent so much on your comps.
if you had bought some cheap speaker then it wouldn't matter.if i where you.
1) Deaden your doors-
http://www.secondskinaudio.com/ there is also fatmat & dynamat
in time you should deaden your whole car, you dont want raddles or your car shaking like a tin can.
http://www.diymobileaudio.com/forum/diyma-build-logs/33715-first-install-lots-pic.html
in this link this guy is doing a full install, but he also is installing the same HERTZ comps that you have, hope you can learn from his install.
2)after you deaden your doors you need to set up which amp your going to use for those comps, like where are you going to mount it, adjust it,
3) if where you i would the BIG THREE, yes ift will help with voltage of your amps & electrical system. your not running enough power to change out alternator & i think your battery should be enough.
4) how is your wiring???
what i'm asking are you running any fuses??? to the battery & between your amps???
not on your amp, to the amp??
make sure you are running the right wires which can play a big part with how your comps will sound.
If that shop installed basic wires that came with the speakers i would at least go up a gage or two.
5) RCA's -with your your front stage they do play a great part into distortion & that hissing sound that you are hearing. So if your running cheap rca's you'll need to replace them.
yes your front stage can & will require lots of work, but now since your becoming a car audio finatik you have plently of time to do it right.
it's all about learning.
your subs aren't going any place so you can put them on hold for now.
you'll be happy in the end.
when you do decide to built a box you can try it yourself or have someone on this forum built it for you.
Remember if you save money by doing things right, you'll be able to spend it more money on your car with how you'll like it to look & sound.
TAKE ONE STEP AT A TIME!