How heavy should the wire be for this?
The wire size depends on the load of your accessories and continuous equipment, but usually this is a 10 gauge wire. But the load determines the size, and high temperature insulation is needed.

What do you mean by"Check my wire"?
I'm assuming you have a wire that is going to the switch, if not disregard.

If this is a new build and you have no wiring in it, I suggest you buy a harness for it.