The quill or feather is used for strumming. I do not think a person could get a satisfactory sound by using the feather as a noter. Something dense and hard would work best for that. A pencil or popsicle stick would work but a dowel would be even better than a pencil.

On the strum there is a theory that the principle strum should be toward the player striking the melody string or pair of strings last. I was not exposed to that theory until I had been playing for a while so I do not play that way. Someone on Mudcat might be able to explain the virtue of the direction or whether it really matters. When a person is just beginning you can use a simple one way strum to get used to the instrument and used to strumming and noting together but as you develop your playing you will also develop a rhythmic stroke with brushes backward and forward. What you do not want to do is a constant backward and forward motion. That can get pretty tiresome for players and listeners. I think Larkin's book discusses the rhythm of the strum. Larkin developed that book from her many years of teaching and she was an exceptional teacher. The book has been helpful to a lot of new players. Since you already have experience with strums and playing music you will probably sense an effective pattern to your strums.

Another factor about dulcimers you have probably already discovered is the tunings or modal scales. I came along before the modern wave of players who named tunings by notes. I learned the tunings by the modal names. The aeolian and dorian are minor scales and sound very nice on the dulcimer. If you progress quickly and have not issues with tuning you might get the urge to experiment with the various tunings.