As to 1), flypaddy nailed it. With higher speed, steering should transition to the rudder anyway. Pushing down on the nosegear with elevator is then not only unnecessary, but can strain its structure (which is lighter than the main gear).
It can even begin to produce "wheelbarrowing" or porpoising (although that is more common with lighter aircraft) - pitch-down force strong enough to lift the main gear right off the ground.
Always treat the nose-gear like a fragile straw.
As to 2), without getting into the various mechanisms of lift (which will immediately lead to 20 pages of thread drift
), the net effect of the main wing is to push air
downwards. That is its
downwash. This can be seen in extreme form with helicopters' rotary
wings - but fixed-wings do it also.
Normally, the tailplane or horizontal stabilizer of most aircraft is slightly above the wing and out of most of the downwash. But at rotation - and afterward, in nose-high climb - when the nose goes
up, the tail goes
down, and is now closer to the downwash coming off the wing's trailing edge (enhanced at takeoff by flap lift). And that changes the airflow pattern over, and the forces and effectiveness of, the horizontal stabilizer/elevator.