Just my opinion but it's extremely unlikely you'll notice any difference between wire for your subwoofers. Get a spool of 12 guage wire at Home Depot and be happy.
Ditto.
My first recommendation was just to look cool in front of the boys, you know.

Agreed with Warner though. About anything reasonable that's a conductor will work fine for sub duties.
Romex, Home Depot (RCA brand), Walmart "Lighting", or any form of "generic" speaker cable etc..... will do fine.
It'll be fine Jim. Just like Las Vegas: Don't spend more than you can afford to lose (if it doesn't meet your expectations).
Bob