I see quite a few builds with the high and low strings spaced out to the edge of the neck (3-string). I've been using a 1/2 inch from center which leaves a 1/4" space in from the edge. What is the pros and cons on the wider spacing. It definitly seems to be easier for slide.
For slide or fretless I just think its important to keep the spacing even. It bothers me if the top 2 strings are spread further apart than the 2nd and third. I feel it too much when strumming. Even sounds nice off the pick too. If I want to build a fretted instrument I usually copy the string spacing on my 6 strings from home. If the Instrument is mainly going to be played with fingerpicking I like the string spacing Taylor uses. 1 3/4" nut width for 6 strings. If I am banging chords and using a pick I like them a little closer together like me Ovation or old Gibson. Which is probably an 1/8th inch narrower??? I havent measured. Look it up online. All the guitar manufacturers will tell you their nut width. Larravie is making a fingerpicking guitar with a nut wider than the Taylor. Too far spread for my little hands.
And dont ever forget. Whatever feels good to you is probably best for you every time.
I do 3/8" string spacing like a "real" guitar, don't worry too much about how close or far it is from the edges. I would say it's like the 1/4" that Randy is showing in his photo. This works fine for fretless and slide.
However, I just built my first three string fretted CBG. You can really hear the frets clicking when you play slide, and you have to change your technique to get a clean sound.
So I was thinking, for my next build to either put the strings closer to the right edge (and not worry too much about the left edge), or make the neck somewhat thinner.
Then I was worried about the stability of the neck with a somewhat thinner neck.
Use threaded rod for temporary bridge and nut. Then you can change the spacing until you find what you like best. Once known replace both with permanent pieces cut to your liking.