Question about making dulcimer soundboard

Hello,

I have just started making the soundboard of my dulcimer out of a solid piece of butternut and I had a few questions.

1) Is there an advantage to adding braces to the soundboard? 

2) what would be the best way to cut out the sound holes using only hand tools? I am planning on making the sound holes heart shaped. Additionally, do the size or number of sound holes effect the dulcimer’s tone? 

3) is it better to glue the fretboard to the soundboard or the soundboard to the body first? 

Thanks so much!

all the best,

Haley Brett