Seems to me folks make two "mistakes" in their dulcimer purchases. Either they start with a 12/11 and almost immediately want a larger instrument, and/or they upgrade or purchase a huge instrument that is cumbersome to haul around.
I've done my share of all of that, but I think now I know that the whole issue is a matter of picking the compromises you want: Want as many notes as possible? Be prepared for large size and perhaps heavier weight. Want portability? Be prepared to live with fewer notes (usually on the low end). Want maximum notes in minimum size? Be prepared to deal with strings closer together and perhaps a less huge sound. Want to play mostly fast music with minimum sustain? Be prepared to give up the ring and sustain that can give slow music on the dulcimer much of its charm. Want to have that sustain? Be prepared to deal with issues of blurring of the melodies when playing fast tunes. All those compromises and we've still ignored the matter of the sound that particular makers get from their instruments.
Linda Foley, long time maker of Lost Valley Dulcimers, says, "No matter how many notes you have there is one more you want." She's right. And, she plays a little 13/13 instrument to great effect. She made her compromise(s). I play my Blanton Compact almost exclusively, and only occasionally miss the extra low notes and wider spacing of my Rizzetta Extended Range. And, from time to time I lust after a Rick Thum or some other instrument with very short sustain for the situations where those work best.
And, remember the difference that hammers make. It is lots cheaper to change hammers than instruments!
So, my advice is start with a decent 15/14 or 16/15 (I'm partial to the Songbird Phoebe), find the "right" hammers, stay with it long enough to have a very good idea of what you want from your instrument and then make the jump while being aware of the compromises...

