How much wire is something that really only you can find out really. Not too hard to get a basic idea though. Example. My '66 plymouth, the cable needed to go the length of front fender + the width of the firewall, then it went into the car. So length of cabin + length of fender + width of car = almost what I needed. Have to give some extra slack for getting around shit in the vehicle.
Wire is one thing that even I don't skimp on. It's re-useable at least. After using it, I will never use anything except this Kicker Hyperflex personally.
0 experience with batteries though.