How can I make a table top with sea shells and sand covered with epoxy
Here are a couple of ideas.
I would not recommend using epoxy which would give it a rigid, fixed appearance unlike the spontaneous freedom of sand and shells. Plus epoxy is difficult to use and expensive. Just have a recessed container for the sand, (picture frame etc. set on top of sand/shell arrangement)
Here is where someone added sea shells to a mirror. This might help. https://www.hometalk.com/7417709/sea-shells-far-from-the-sea-shore-a-mirrored-view
You would need to build a frame, glue in the shells, and then fill with epoxy. Probably pretty expensive for that much epoxy.