Thank you for your kind interest. Here are the answers.

1. I don't sing to the dulcimer. I play DAA because I like the richer, warmer sound of a low pitch.

2. The D is the lowest note.

3. The string gauges are what D'Addario provides in its dulcimer string package. They probably think I will tune DAD, but the gauges work for DAA as well.

4. String lengths - all strings are the same length on a given instrument:

    McSpadden (DAA) 72.2 cm from nut to bridge
                      71.8 cm from first fret to bridge

    Cedar Creek (GDD) 70.2 cm from nut to bridge
                        69.9 cm from first fret to bridge

I hope I measured the right thing.