1: I don't know, but my guess is you could change the Pitch Mixing in the radio, that ought to be explained in the manual.
2: If you leave out the Gyro, then the Tail engine is only controlled by the rudder stick input.
3: Gear is up/down function on the gear channel of the receiver. Typically used for operating the landing gear on a plane.
4: If you use a Speed controller with reverse (0 speed would then be stick centered) Heli Speed controllers doesn't have a Reverse, as they have no need for it.
You should be able to find manuals at:
http://www.walkera.com