fretboard sequence?

Looking through all the discussions and other info on the internet, it looks like the sequence while making my fretboard will be something like this:

1. measure for fret placement
2. cut slots for fret wire
3. install fret wire
4. apply tung oil to the top of fretboard

1] Or should I apply the tung oil sometime earlier in the sequence?

For my cigar box dulcimer, the fretboard will be held in place by screws to the boxes (but may be glued at some future date).

2] If I polyurethane the sides of the fretboard, do you think there will be any problems at the edge between the poly and the tung oil?