#1
my neck is relatively straight and not bowed but the action is too high, it is really difficult to play this guitar now. i got this for cheap, at around $50.
#2
I think sometimes there are shims under the bridge, gotta take the strings off and pull off the bridge to see...if not, maybe shave down the bottom of the bridge...not speaking from experience here....
#3
It was probably done on purpose, if you lower it you'll probably have fret buzz,etc
#4
The action is set on an accoustic by adjustment of the bridge hieght and the truss rod. The truss rod should only be used for fine adjustment since the ideal neck is very slightly bowed. Put a capo on the first fret and hold down 17th fret, there should be no more than 1/16inch action at the 9th.
#5
There should be a sticky on this. Stay away from that truss rod. Go to Frets.com and read the section on "Instrument Set Up"

http://www.frets.com/FRETSPages/pagelist.html#Musician
It will give you all the standard directions and measurements for setting the action on an acoustic guitar.
If yours is out of specification, you can then take it to a tech or do it yourself. Special tools are required.
#6
Truss rod for neck relief to prevent mid-point of string from slapping the frets during movement. Bridge adjustment for raising/lowering action