fmarty, nuts drive me..well...nutz!, they are a serious amount of work and time to get right,plus any precision files you'd buy for this are around about the cost of having 2 or 3 professionally cut nuts installed.

I advise bone or brass for good tonality and sustain on a guitar with a fixed bridge, graphite can be good for trem equipped guitars.

The lower strings should sit "about halfway out of the nut" and and the highest should be just about all the way "in".

How's your playing advancing?