Mountain dulcimer is dead easy to play simply. You get a 'noter' (stick) and use that to fret the string. You can probably play harmony notes as as a bit of an arrangement if you want.

It's not so easy to play more than just single note lines with open strings. Lorraine Hammond can play damned near anything, fiddle tunes, bluegrass, and devastatingly beautiful accompaniments. Mostly though it's a great instrument for allowing you to make the music in your head a reality.

It's not chromatic though, so you can only play in one key unless you re-tune the instrument. If you're only accompanying yourself, and you usually only play in D, you're fine.

I like Chlorox bottle triangles for picks. They're about as stiff as quills, and easier to come by, and people don't swipe them for some reason.