Currently the recommendation is that the lowest line be 8" off the ground and the highes between 54"-60."  I had two adult horses on 1.5 acres of land, broken up into 4 pastures and one "round pen" paddock-y thing.  We ran two Electrobraid lines, one at knee height and one at boob height (yeah I know, real scientific!!!).  I am 5'4" if that gives you an idea of height, probably two feet from the ground for the lower line and four feet for the upper one.  

Bird spikes are great if you can get enough for all the "perch" places-


I know they make fake owls with motorized heads that turn (really freaks out the birds), but other than that, I have been dealing with birds for 7 years and never knew how to get rid of them.  Now we don't have the horses anymore so I am not fighting that battle!