I use 42 mm (1 3/4"), but 1 1/2" will work fine if you are OK with a slightly closer string to string spacing.
neck width is personal prefference, there is no golden rule. Iḿ a lowender and on my 4-stringed BC Rich Warlock neck width is 42mm, on my daughters 4 stringer and a Höffner shorty it's only 40mm. Maybe try some guitars out with different neck widths to see what you like.
The standard 1.5 is enough, especially when you think of the distance between strings on a six string. Now someone did once tell me that you could widen the distance between the strings at the bridge for fingerpicking, but I never tried it.