Avoid splicing motor power cables when ever possible. Ideally, motor power cables should run continuous between the drive and motor terminals. The most common reason for splicing is to incorporate high-flex cable for continuous flexing applications.
Shield drain wire must be spliced only to mating shield drain wires and not grounded at the junction box. Feedback shields must be passed through pin for pin. Separate junction boxes for power and feedback are required.
Here is where metallurgy comes into play. A motor rich in magnetically soft material will be more efficient, producing more work with less heat. And since the magnetic capacity of a motor also is influenced by the amount of active material (more core, more laminations), the tendency might be to try to add as much magnetically soft material to your design as possible.
A simple, experimental motor such as this is not capable of making much power. We can increase the turning force (or torque) that the motor can create in three ways: either we can have a more powerful permanent magnet, or we can increase the electric current flowing through the wire, or we can make the coil so it has many "turns" (loops) of very thin wire instead of one "turn" of thick wire. In practice, a motor also has the permanent magnet curved in a circular shape so it almost touches the coil of wire that rotates inside it. The closer together the magnet and the coil, the greater the force the motor can produce.