<VV> Air compressor/Line q (No Corvair)

[D. Barry Ellison]

I'm in the middle of building a garage but I need my air compressor like NOW!  I'm tempted to mount it outside and run lines into the attached garage.  Then later run lines to the new 3-4 car garage out back when it's built later.  I'm worried about water build up in the lines.  The garage will hopefully have numerous access points in the working area.  The garage will be as close to the house as possible, about 25-30' from the compressor.  I'll build a room attached to the house around the compressor to keep it safe from being stolen mainly.  
 
A) Would you run lines underground?  Is this a water/humidity issue for cast iron?  This is SC so the humidity is quite high.  Constantly draining my lines/filter when it's running.
 
B) Would you run PEX instead?  Copper?  (I know better than to ask about PVC. <gg>)
 
C) Would a filter coming out of the tank be enough to keep the lines clean for both access points?
 
D) Any other suggestions re:filters, humidity, material choice?
 
Thanks for your experience.  Trying to get the most usefullness from my tools w/o redoing my work.  I do enough of that with my corvair work. :D
 
Guess I could always move it to behind the garage at the back of the property at a later date, add my room on there.Barry in SC (actually hospital waiting room.  Mom had quadruple bypass and not doing well)