I really like it!
I also am impressed with the way you did the buttons. I'm still slightly unclear what you did but it looks like a great idea...
Basically what you do is cut two pieces of plexiglass to the size you want. Hold the tact switch where you want it on the back piece. Mark the 4 leads of the tact switch with a marker on the plexiglass. Now drill out those 4 spots with a small drill bit. Dab some superglue on the bottom of the tact switch and the plexiglass between the holes. Push the tact switch onto the plexiglass and hold till it is stuck. Now on the second piece you will cut out the button holes. You want them to be a bit larger than the buttons. Just set the piece in the case over the holes in the case and mark the centers with a marker.
Now you want to attach the two pieces of plexiglass together at the right height. So determine how far apart they need to be and then glue spacers on the 4 corners so they stay that far apart. I found spacers of the perfect size from a craft shop. They are jewelry spacers that are put between beads on necklaces. They come in many shapes and sizes.
Then when it is dried, position it in the case and PlexiWeld or Super Glue it down on the case.
Once you do one or two it is a piece of cake