Helical antennas and orientation
First, a caveat - I'm primarily a CE, so this is just my understanding of the matter:

1.&nbsp;Generally, the worst reception is when the antenna is upside-down, or nearly so, and the best is when it is vertical.  However, horizontal orientations are nearly as good as vertical; the radiation pattern is usually something like this, with "up" in the picture corresponding to the positive Z axis (defects overemphasized): 



2.&nbsp;Again, your antenna manufacturer will likely have a reference design for this.  Sarantel publishes sample gerbers for many of its antennas.  If the antenna is not directly coupled with a ground plane, near-field radiation will still be helpful.

3.&nbsp;No idea.  I doubt that it would matter as long as both antennas had decent signal strength.  Back-to-back might not be ideal, but everywhere else should work fine.

4.&nbsp;No, it's hardly directional at all.The reason you use a helical antenna is because you want near-omnidirectional performance.  If orientation is controllable, use a different antenna.