A Programmable Digital servo's deadband can be programmed to stop any hunting. They don't hunt unless you have the deadband set to 1. Even then, I have never seen one actually moving. They just chatter/buzz a bit w/o damaging the servo.

The torque necessary depends on weight on the tire, size of the tire and length of the servo and steering arms. But having metal gears is a good recommendation. Also programmable servos have torque limits that can be programmed below the max spec of the servo. Kind of a servo saver setting. Ever seen a nose wheel that did not turn when the jet was sitting still on the ground and the stick was moved? If yes, that servo was stalled. W/o having the torque limit set below the max spec, the servo can fry.

Also, mixing the steering to the gear switch so that the servo is not enabled unless the gear is down can prevent the servo from being stalled when it is retracted and bumping up against fuse as it tries to turn.