Ok first of all, as much as I have researched car audio systems I'm still pretty clueless when it comes down to the numbers side of it

In the old VT I have thrown in a bit of everything, it started out with a very basic Alpine package but most of that is gone now

I am currently running

Headunit - Clarion Australia | CZ500A

Amps - speakers Xa125 - 4 Class AB 4-Channel Amplifier - XENITH SERIES - Cadence Acoustics, LTD
and for the subs Kenwood - KAC-8105D

Speakers - Alpine Electronics of Australia
and DS Series | KICKER (DS600.2)

And now the subs - All I know about these is they are Kenwood 2x 12" and look like

It's all in my car and working.. Just working :P (backyard jobs ftw)

Now some questions
1) Anyone have any idea what model the subs possibly are?
2) Should both amps be running off a 4guage power wire?
3) If we do figure out what the subs are, am I underpowering them?
4) Same for the speakers, underpowering/overpowering?
5) SETTINGS! The H/U has so many of them and I have no idea what half of them do, I have the basic idea of LPF/HPF but what about "Mid" and all the other funky ones, a list or guide would be great.
6) Fader and Balance don't work right, I'm guessing I should be running 3 RCA's instead of 2? (1 for sub 1 for speakers, only had 2 at the time) Do they even have anything to do with it?
7) This is probably a personal choice but what is the normal settings for a sub? On the H/U or the Amp.

That's all I can think of at the moment, remember I'm a noob so go easy on me

Any advice would be great.