chaotic yeti

Greetings! This past Friday I installed an AVIC-D3 in my 02 wrx. It was the first HU, speaker install I've ever done, and it went without a hitch. I'm having a custom sub enclosure made, and will be purchasing an amp and sub shortly. I just want to clarify the connections made to the HU. RCA to sub inputs, and amp control wire: is that all there is to it? What gauge wire should I use for the amp control?