Diamond system feedback

A few questions - what kind of sound are you shooting for?  Why are you sealing the box interior if it's vented - SPL?  What makes you think you need a HO alternator with only 1k watts?  And why the extra battery?

I think your stock alternator will be fine with that load so unless you just want the higher output for something else I'd save your money, maybe put it towards dynamatting the doors, that'll give you a better return.  2g wire should be fine too unless the amps live in a trailer 30' behind your car.  You're going to have a ton of bass & limited mids given the power differentials & box design, but that may be what you want.  The extra battery is only helpful if you plan on running the system with the car off - that the plan?  Be sure to use an isolator if so  Anything for rear fill?.

OK, so like a typical engineer you've waaay over-engineered this system IMO...

If you're looking for SQ I believe you'll be disappointed by the boomy nature of a slot-loaded box, sealed would do you better, again, IMO.  You've got the power & it would balance things out better.  I think the FG sealing is a waste of time here too. 

So you're actually showing your front amp an 8 ohm load?  Unless the amp has a regulated power supply your mains will be way underpowered.  Better would be 100w x2 up front & a smaller second amp to the rear (35-50w x2).  the same 2g wire will handle that fine.  Again, this would help balance the system out more.

About amperage draw, it should be more like 100 - check the fuses on those amps.  wiring above that will never give you an audible difference.  Same for the spare battery.  Besides, if it's isolated it won't matter, it's "off" anyway.  Nix it.  Last , remember the max amperage draw is exactly that - max.  Unless you're running the system really hard a lot of the time, you're really only drawing a fraction of the current.  There's nothing inherently wrong with overbuilding it, but there's no real gain either.  Good luck.