I bought my only dulcimer three weeks ago. You will appreciate that I am unable to offer technical advice relating to how it should be played
I am Welsh and love Celtic music. I would like to draw attention to two pieces of music written in Wales. I really don't know if they could be arranged in a form which is suitable for playing with a dulcimer but, even if they are not, they are very beautiful and I am sure that people here would enjoy listening to them. I am not allowed to post YouTube links here and will refer to the music by description which enables a search to be made.
The first is "Dafydd Y Garreg Wen" and was written , allegedly, by David Owen as he lay on his death bed. The YouTube version I recommend is that performed by Hannah Thomas and Catrin Meek. There are many versions available but this is my favourite.
The second is "Myfanwy". I have to admit that I am totally biased as I drive past the house where the music was composed at least twice a day. Additionally, I had the pleasure of meeting Ryan Davies in 1968 when I was a student at UCW Aberystwyth. He was a very nice guy. I have chosen his version as my favorite (American spelling this time).
Sadly, like Dylan Thomas, Ryan died in New York State at a very early age. I hope you enjoy these two wonderful pieces.