Sounds good. I might have to buy some more 4AWG to run from the (-) amp to the battery. Although the amp I am looking at takes 0-2AWG

If it takes 0/2AWG, use it. It probably needs it! Its always a bit of a hint

Using cable which is too big will never hurt you, and at the end of the day it may be the difference between good sound and great sound. Do it properly once, the first time.

The other thing to think about when speccing your electrical system is what are the fuses on the amps rated at. This gives a great indication of how many batteries you need, and what sort of wiring and distribution scheme you need. If you wire your system according to the fused capacity of the amp, you know you'll also have built in a little bit of head room.

Sorry, that last post was probably a bit confusing! My current amps I've got some decent 4AWG, but the one(s) I am looking to purchase will take no less than 2AWG.

How will the fuses tell me how many batteries etc I might need? That's news to me. But I am trying to cover all bases first!

The fuse rating of your amp shows you the Current potential. Sure the amp shouldnt reach the fused rating in normal operating conditions, but it may reach 80-90% of that.

If you've got a system which draws 250A, then you need to factor that into your battery and alternator requirements. Maybe an alternator bigger than the 100/110A which is found in the EL/EF would be desired in this case, and maybe a few high capacity Deep Cycle batteries would be handy to ensure you can run the system for a good 30-60 minutes at full capacity without flattening the battery.

Lets face it.. a standard 500 odd CCA lead acid batery wont last long driving a system which is sucking 250A