Come to think of it, you will need to disconnect the motor wires so the motor doesn't just hang there. But again, two screws and the motor wiring is disconnected. There is no polarity, so orientation is unimportant when replacing the motor wiring. The power wires to the speed controller do not need removing to place the hand crank.
I like to use 16 gauge wire. Sometimes the original are 18 gauge but 16 is larger and I can think of no negatives using a heavier wire.