The switch won't care which way you wire it. The switch with the speed control resisters won't care which way you wire it. Use the screw closest to the heater to run the heater. Use the screw closest to the drop resister to run the switch. Won't hurt a thing. Fuse according to the wire gauge that is on the motor and make all of the other wires the same. My best guess, 30 amp with 14 gauge wire. Put the fuse in front of the drop resistor. That will protect all of the parts you have in the system. Remember that fuse size is just a guess. Check the wire on the motor for sure. Look at the amp rating on the motor as well.

Steve H