Recommendations for new strings and new a bridge?
Instruments- discuss specific features, luthiers, instrument problems & questions
For string gauges, I usually send people to the Strothers' String Gauge Calculator . You simply enter the vibrating string length (VSL, or the distance between the nut and the bridge) and the note you want to tune to, and the calculator will tell you what gauge to use. It errs on the light side, so feel free to use a size or two larger.
For a dulcimer with a 27" VSL, I would imagine a wound .022 or .024 for the bass, . 012 or .014 for the middle, and .010 or .012 would work for a DAd tuning. I use slightly heavier strings than that, but you'll have to discover your preference.
The bass string is almost always wound and heavier than the others, but if you are tuned DAAA, then the melody string(s) and the middle strings would indeed be the same.
I don't really know what to say about the material for the bridge and nut. Hardwoods work well but so does bone, and there are some synthetics that people are using these days as well. Maybe one of the luthiers can chime in and offer some advice.

This is the one I like for the FOTMD Family!
is pure Strumelia, for sure!
but also the dancing guy silhouette
Let's pretend that's a hamster chew toy smiley.
. It almost makes me tear up.
... lolol!
yesterday.
,
, and
.
today and I just finished
certain smileys or if they just make you want to