[KMC3420]

I am in the planning stage of plumbing my brake lines and I have decided to go the NiCopp route. My truck is a 68, converting to 5 lug and disc/disc. I haven't decided on a master cylinder yet.
Few questions I have below:

1. Are there specific fittings for NiCopp lines? I keep seeing reference for Black Oxide fittings as opposed to Stainless or Brass. Wouldn't the Black Oxide fittings be steel?
2. Is it acceptable to use 3/16" lines for each hardline, or do I need to use 1/4" lines at any point? I think the lines that run across the rear axle were originally 3/16", but the rest were possibly 1/4"? .
3. Any suggestions for a disc/disc Master cylinder?

Thanks!