Thanks for writing. The project turned out wonderfully and I managed to get it done for Christmas. It was a present for my grand daughter, but I am sure my daughter will probably play it more.
I deviated from your orignal plans. For starters I used a birch faced plywood for the box and bottom pieces. 1/2 inch and 3/16 inch respectively. I like the look of wood better than paint. On the front and rear joints I used box joints rather than a butt joint. Instead of the divided stepped bottom I used a slanted bottom. Deeper at the lower notes and shallow at the high end. The box joints didn't turn out as nicely as I'd hoped so I used some purple heart to accent the corners of the box and to hide the joints. The top edge of the box I used some press on birch verneer to hide the plywood end grain.
For the note bars I used paduke wood that gave the notes a nice clear ringing sound. For the note bars I drilled parallel to nodes at the node point and supported the bars using 1/8th inch nylony line. To divide the bars and to keep them from slipping I used small surgical rubber tube cut to keep things seperated. The picture I sent doesn't show the rubber tubing as it was taken just before I packed it up to take it out on the plane. Final assembly was done at the house when I arrived. The line is tightend using the turnbuckle and supported using the eyehooks. The whole thing was finished using only a couple coats of Danish oil.
Thanks for the plans.