engine electrial

Hey, I am looking to upgrade my 2007 ford focus SE 2.0l's electrical for my system. I have a 5000 watt sub amp and a 600 watt door amp. I know I'm running the stock alt, so that's 120 amp max. Aka that's around 1600 watts max. There are 2 4 gauge wires running to the amps. I'm looking at a 370...