We are extending the thread here, but working form the string side is OK if you have a false fret to put against the nut, at the height you require the slots to be. Easy on a nylon string (if flat fretboard...) but a hassle on any radiused neck. And, one would want the guitar to leave the factory with the correct setup, anyway.
Bone nut is a must-do, fresh bone work better than sun-dried/bleached pickups. Only hassle is the rather sticky dust. For nut files, modify several mini-hacksaw blades, grind off normal hacksaw blades, and save old wound strings to help saw/polish. Some small needle files help to, you can grind flats on the round ones to make a "nut" file giving a sort of rounded bottom slot. Sort of. Hmm, and buy a "jewelers saw", those blades are very thin, just right for light gauge trebles. For perfectionism mill out guide slots at exactly the correct spacing. For DIY, vernier caliper, pencil, saw.