Yea, youre not going to need a 2 gauge wire for that. 4 gauge will be more than enough + some overhead. And if your electrical system is in good condition, you shouldnt even need a cap.

With that said, I think you should pick a different subwoofer or get a bigger amp. The W7 is a huge beast. It likes a lot of power, and I think for the price you pay for it, you would want to take advantage of that. 500 watts isnt going to cut it. I think if you were to keep that amp, getting a smaller, less power hungry sub would be a wiser choice.