Hey everyone, so I have a 2017 wrx base audio, it’s terrible. I have an oldish 80 watt powered sub (sound ordnance b-8p) and an alpine KTP-445U. My plan is to use the alpine to send some power to the speakers, and put the sub in the trunk. I have no idea where to get started. I know I’ll need to get some sort of distribution box so I can split the power. The alpine will prob be located in the glove box or behind the head unit. So my question is, how do I go about splitting up the power and grounds. What size wires should I use? And the necessary hardware?

Thanks in advance.