Good question(s) Hibuke
Here's the deal, I used to stick exclusively to U.S. made files like Nicholson or Simond's, thinking, erroneously, that there'd be a big difference in quality over inexpensive imports. I've since used plenty files from India and China, with consistently good results. In fact, if I don't have time to go hunt for used files, and find myself purchasing a new file to make a blade from, I'm more than happy buying the ones from India (Sunflower files, sold by Ace Hardware under the euphimistic trade name "Vermont American"). They're all made from fine grained, high carbon, tool steel, or else they'd be a poor material to make a file from.
In picking out a file, new or used, look for the finest toothed file you can find (flat smooth or mill bastard). Coarser teeth require cutting into the metal deeper to produce, and you'll wind up doing significantly more stock removal to get your blade blank smooth (read that wasted time, wasted material, thinner finished blade).
Most important thing to remember, if you don't have access to sophisticated heat treating equipment, is to preserve the hardness of the blade by grinding slow and dipping in the water bucket often. Don't use gloves, pliers, or anything else but your hands to hold the blade when grinding. If you pay attention, your finger tips will tell you the blade's getting hot long before you burn the temper from it (indicated by localized discoloration at the hot spot). The exception is when working in the area of the edge/point. Here the metal is thin enough to develop excessive heat quicker than you have the ability to detect it. Slow, careful, and very light pressure is the key here.
Hope I've been helpful
Sarge
