#1
Is there some way of anticipating at which point you'll get fret buzz when adjusting the height of the saddle? I mean, before you actually start sanding the thing.
Dear God, do you actually answer prayers?

Yes, but only in a way indistinguishable from random luck or the result of your own efforts.
#2
We really should "sticky" this....

Go to Frets.com:

http://www.frets.com/FRETSPages/pagelist.html#Musician

And read the "instrument set-up" pages. This will show you how to make the standard measurements for an acoustic guitar, how to mark the saddle, etc.
Note that you cant just go flailing away with a sheet of sandpaper, you need to use a sanding block to keep the bottom of the saddle absolutely square.
Also, saddle height is only half of the action equation. You must adjust the action at the nut, and usually that should be adjusted first.
Many guitars are shipped with the action rather high so that musicians can adjust to their own taste.