So apparently I'm an idiot and wasting my money on OFC wire, CCA is just as good. OFC is only needed with high fidelity amps, not large current draw... And two runs of 4ga has more power transfer than a single 0ga run....
250a its the max rating it can handle before damage. 20ft ofc 1/0 will likely not pass more than 125a. That's why big power applications don't just have 1 run each on alternators. You should have at least 1 run for every 100a.