That's a very neat idea! If you're wondering what diameter top you'll need to seat 6, the guide here can help you. It shows that you'll need a top between 4 and 5 feet in diameter, with 5 feet offering more ample space. However, glass is heavy and it will be trickier to determine whether your vase can support the top's weight, and even trickier to support the glass so that it doesn't tip when something heavy is placed on one side of the table. I think you'll need to manufacture some kind of support that attaches firmly to the vase and then extends out to support the edges of the table top. That would unfortunately do away with the floating look of the glass top.