wire thickness

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?

A few years back I had 8 gauge wire ran from my battery (with an inline fuse close by) through my firewall back to my trunk where the goods are. I have the + 8 gauge wire ran straight to a capacitor, and from the capacator there are two 8 gauge wires ran to (a) HiFonics 1000.d amp for 4ohm sub...