Eww, metal dowels? I use a wooden dowel at the head and a true bridge placed so that the fret board is properly tensioned and does not warp, takes some practice. The fretboard floats about a 1/4 inch above the soundboard. The fretboard becomes part of the vibrating part of the instrument and adds (or detracts) from the sound. This is different from the neck of a guitar.
As far as the soundboard goes, yes, you need to practice bracing so that you emphasize the sound you are looking for. If you are building a standard (treble) dulcimer, try thicker and more bracing. This will dampen the bass and give you clearer melody notes. For a bass (my favorite), try longer thinner bracing so that the bass can vibrate. (The shape of a MD allows for much longer bracing than most other instruments, a difference that can be used.)
If you have difficulty placing the bridge properly, try a second bridge under the seven fret. A wooden bridge still transfers vibration to the soundboard. I prefer lighter wood like cedar for my bridges, but like everything a luthier does, whatever works for you is best.
If you are going to try this, you might want to subscribe to American Lutherie. This magazine focuses on the guitar, but you will find lots of articles by people who have been shaping bracing for years.