I don't know what damage it would cause, DC-3s have snubber strips in the wheel well to keep the tire from turning, we never tapped the brakes.
The 727 only has an air/ground sensor on the left main and nose gear. The nose gear works with the stearing, everything else is from the left main. 747 has tilt sensors in each truck plus the nose gear air/ground. Once you're on the ground and deploy ground spoilers, everything is going to come up, you're not worried about the crosswind.
Why, you'd just have to air the tire up again.
Pins are used when they're used. Whatever the operator's manual says. 747s have gear pins. The mains on a 747 or 727 won't retract on the ground even if you move the handle to "UP", they'd have to lift the aircraft. I know the nose gear on a 727 will retract, not sure about the 747.
"OFF" just removes pressure from the system. The 747-8 won't have an "OFF" position.