I would use a 50 amp breaker just in case. The breaker will save your motor should something happen. Then you just push the switch to reset it if it trips.

Electrical is like this:

The motor will only use the amount of amps required to create the power it needs. But after time the brushes wear and creates more ohms (resistance) so it will take more amps to create the same amount of power to turn the motor. Think of electricity like water flowing in a hose. Voltage flows with no resistance. Amps push the water through the hose when there is resistance. When you kink the hose it creates more resistance and then you will need more amps to push the water through the hose.

The fuse or breaker is designed to protect the circuit from over amperages that will burn the intede source of the power. Once you burn the circuit either the wires or the circuit board/motor it is damaged. It may still work but not to it's full potential. Once you let the factory smoke out of the circuit it's done. (all electrical components come equiped with smoke inside from the factory so don't let it out :D)

If you guys ever have any electrical questions just ask me. I have a ton of electrical knowledge from my time of auto repair with Toyota and several other automotive repair shops.