What gauge wiring required for this setup?

honestly i would go with 2 gauge and utilize the capacitor because you will probably not be satisfied with just 1- 4 channel amp and you will most likely want to add a separate amp dedicated to just subs do then it would be beneficiary to have 2 gauge and you will not notice a db gain from the capacitor but it will increase the punchyness of the b and increase the life of your alternator/battery because its like a quick discharge battery and helps hold peak voltage under a heavy b note which is where your wiring will be under its heaviest load and the lower the note the heavier the load