In this picture, the light purple is the work area and the green is the build area. The top glass can be any size in between. But most likely, it will be close to the work area. The red corner parts have to screw into the bottom of the table and I doubt you want them screwing into glass. So if your bottom is glass and it is the same size as the top, then the glass will be close to the work area.
In my table top version, I sandwiched 3 pieces of ply to make a deep recess for the leds. I like using glass under the sand to get a flat and rigid surface for the ball to ride on and the magnet to fly under.
The table pictured is by Ryan and there are a few details here:
I think that is the wider version of the glass I bought. The border is not small, so making the table too small makes it feel weird. But the table I linked feels natural (a bit like a 4:3 screen). I have brought it to two shows and it actracts a ton of attention. Everyone is interested in it. The addressable LEDs are quite flashy.
That should be good. It is based on the total table size, so you could cut a hole in an existing table.
I tweaked it a little and I couldn’t select the non US version on my mobile for some reason. But I tweaked it until the “actual area needed” was 12mm smaller than your glass (to give some room for a lip to hold the glass up).