How many coats of finish/tru-oil do you put on the board? Enough to seal it I would think?
With maple I put as many coats on the fretboard as I put on the back whether I'm doing a hand applied finish (Tru Oil/wipe-on poly) or spraying lacquer or poly; satin or gloss.
You can do as many or as few as you want. Like many parts of guitar building, there's no set rules necessarily (mainly recommendations) and it depends on what you wish to achieve.