Sizing a motor and gear ratio for a robot joint

You are sizing the actuator for a single revolute joint on a robot arm. The joint must hold and slowly move a load that requires a peak output torque of $12\,\text{N·m}$ at the joint, at a maximum joint speed of $30\,\text{rpm}$. You have selected a brushed DC motor whose continuous-rated output is $0.20\,\text{N·m}$ at a rated speed of $4500\,\text{rpm}$. Walk through how you would choose a gear ratio and verify the motor is adequate. Discuss torque margin, speed feasibility, and at least two real-world effects (e.g., gearbox efficiency, backlash, reflected inertia, thermal/duty limits) that you must account for before committing to the choice.