One best practice is to consider spacing to be part of drawing, not something you do afterwards. Glyph is the black and the white 
You can find some tips in this recent discussion.
I find it easier to keep in one file if it’s meant to be “variable”, even for large 300-styles font families.
Spacing and kerning can be reused to a good extent (especially if you use metric formulas smartly), but this video can give you an idea of problems to expect.