The pilot hole for the tailpiece needs to be small enough that the screw does not move when tightened, but not too small that you crack the endblock. 2mm seems to work on the hardwood I had but a smaller hole might be more likely, so please test on a scrap piece. If you can, drill an smaller hole initially and then the hole size you need(avoids splitting the endblock inside) If you did make the hole too large you would need to get a larger screw for the endpin, maybe needing to enlarge the hole in the endpin.
The ebony/rosewood insert isn't necessary, though over time may prove beneficial.
I will be using a plain maple bridge during my setup.
The strings used for this tuning and this scale was 10.14 and 23 wound strings, basic Stick Dulcimer strings that you find on several models out there, this is quite low tension and great for the neck with no truss rod, I have in the past tuned to G, using thinner strings at a higher tension, one advantage of the Gdg tuning is that you have no wound strings!! I measured the strings lengths in the videos to show how I compensated the bridge, angling it. It is a compromise as the Bass string is a touch sharp, but I find that the middle string it more important to get perfecty in tune.
I didnt need to touch the fingerboard, In the past I have needed to flatten the frets and crown them over again but recently I have been simply pressing the frets in, filing the edges and finding that the fingerboard was good to go, It may be that I am using the right fret saw and the fret press now, though I hammered one fretboard by hand and had the same result.
I add a few millimetres to the length to compensate.
The nut to bridge measurements after compensation:
D3 string 655.5mm
D4 string 654mm
The strings are still settling in but I couldnt resist improvising and having a good play. I havent played a stick Dulcimer for a year now and I don't have anything new to play just yet, I will learn a couple of pieces and do a tutorial for them when I can. The sound has its own quality, you can get a breadth of expression from it,