wire gauge

Hello, I want to connect a TRF VLSW123D2 Subwoofer (250 watt RMS) and my front JBL Stage 2 604C (45 watt RMS each) to a TRF M600.4AB amplifier (4 channels, 600 watt RMS). What gauge wire should i use for the subwoofer and what for the speakers ?

On thw back of my pioneer head unit cables are 0.75mm2 and I want to connect them to 2.5mm2 speaker wire that goes to the back speakers,I used thicker wire because it is 5m long. Is it bad or is it dangerous for head unit to mix these 2 speaker wire gauges?

I have just upgraded to a Pioneer 2400w mono block and I have a single 12' Pioneer Champion. The sub is wired with 16 gauge speaker wire at 2ohm. Is it dangerous to to have such skinny speaker wire with 2000w? Side notes: -Amp Power/Ground 1/0 gauge -speaker wire does not exceed 4ft from amp

My question is basically this: what does the current look like(not actual LOOK) from the alternator to the first battery? Is it the same as from the second battery and to the amplifier? I want to run two batteries in parallel and try to not have to upgrade my wiring. I have 4 awg wire running...