Isn't this sweet? You could make a bunch of these, or just one like I did for my most recent birthday boy. I really like the idea of a special glass for the birthday child, (and he was thrilled) and it works quite nicely with our birthday chair cover (here)! So whip out the brand of epoxy you know and love, and if you don't know or love any of those extra strength toxic glues, so ask at the hardware store. Crafters in the US seem to love some brand with the number 2000 in it.
And for practicality, I would recommend not covering the rim for ease of cleaning and comfort of drinking. and yes, gluing things to a round surface does take some patience unless you can find a super tacky glue wherein the buttons won't slide around like mine did! I worked in sections, with the glass lying down, turning the glass after the buttons on top seemed to be adhered. Of course the results are so cute, a bit of futzing around is worth it!