If your floorboards are visible in the ceiling you’ll want to put up some drywall or something on the ceiling, every time someone walks on the floor above, some dust will get knocked loose and fall from the ceiling. You could put up some drop cloths as well for a quicker, less permanent solution.
I would think that you could leave a Rosetta Stone with directions on how the data is stored and read. It wouldn’t take much, I think. “These glass things contain information, here’s how it is encoded. Here’s the requirements on reading these”. You could start off simple and have a rudimentary one that can be deciphered by hand that describes how to make a device that can quickly pull information from a few others that give directions on how to build another device to read the high capacity ones. You don’t need a specific filesystem or computer to read it, you just need to know how to decipher it and that it IS data stored in a certain way, not just cool looking glass art.