Hi Fred
Sorry for beeing so late with my answers:

1) and
2) I went to a thrift shop, there I found diffrent plates and with my DaTuner App on the smartfone I was able to found out the exact tone of the plate in the chromatic scale. I tuned the plate with an angular grinder by reducing the diameter of the plate, this moves it to a higher tone (to a lower tone is not possible).

3) I did many tests for finding out the right solenoid, the distance to plate, the length of the solenoid impulse, etc..

4) I used a rubber pulse damper for fixing the plates. To reduce the swinging amplitude I put e small PVC tube arround the damper.

5) I used MIDI songs from the interner, e.g. from http://midimi.org/

6) At the moment I can select two channels from the MIDI File to play on the piattuino

7) Of course a e.g. two line character display would be more comfortable, but to keep it simple, I selected this display

Many Greetings
Heinz